Electrochemical actuator

ABSTRACT

The present invention provides systems, devices, and related methods, involving electrochemical actuation. In some cases, application of a voltage or current to a system or device of the invention may generate a volumetric or dimensional change, which may produce mechanical work. For example, at least a portion of the system may be constructed and arranged to be displaced from a first orientation to a second orientation. Systems such as these may be useful in various applications, including pumps (e.g., infusion pumps) and drug delivery devices, for example

RELATED APPLICATIONS

This application claims priority to is a continuation-in-partapplication of U.S. patent application Ser. No. 12/035,406, filed Feb.21, 2008, the contents of which are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with the support under the following governmentcontract: W911W6-05-C-0013, awarded by the U.S. Army. The government hascertain rights in the invention.

FIELD OF THE INVENTION

The present invention provides systems, devices, and related methods,involving electrochemical actuation.

BACKGROUND OF THE INVENTION

Actuation generally refers to a mechanism by which an object, or portionof an object, can be adjusted or moved by converting energy (e.g.,electric energy, chemical energy, etc.) into mechanical energy.Actuators may be categorized by the manner in which energy is converted.For example, electrostatic actuators convert electrostatic forces intomechanical forces.

Piezoelectric actuation provides high bandwidth and actuation authoritybut low strain (much less than 1% typically), and requires highactuation voltages. Shape memory alloys (SMAs), magnetostrictors, andthe newly developed ferromagnetic shape-memory alloys (FSMAs) arecapable of larger strain but produce slower responses, limiting theirapplicability. Actuation mechanisms that are based on field-induceddomain motion (piezos, FSMAs) also tend to have low blocked stress. Theabove actuation methods are based on the use of active materials of highdensity (lead-based oxides, metal alloys), which negatively impactsweight-based figures of merit. Thus, there is a need for a technologycapable of providing high actuation energy density, high actuationauthority (stress), large free strain, and useful bandwidth.

Certain methods of actuation using electrochemistry have previously beendescribed, wherein the load-bearing actuation materials are in gaseousor liquid phase and may be expected to have low elastic modulus andconsequently low actuation energy density and actuation stress, comparedto the approach of the present invention. Despite the observation ofdisplacement, mechanical work has not been demonstrated.

Accordingly, improved methods and devices are needed.

SUMMARY OF THE INVENTION

The present invention relates to actuator systems constructed andarranged to be displaced from a first orientation to a secondorientation comprising at least one electrochemical cell comprising anegative electrode and a positive electrode, wherein one or both of thenegative and positive electrodes is an actuator, and comprises a firstportion and a second portion, and wherein upon charge and/or discharge,a species is intercalated, de-intercalated, alloys with, oxidizes,reduces, or plates with the first portion to a different extent than thesecond portion, and experiences a resulting dimensional change relativeto the second portion, thereby imparting to the actuator a differentialstrain between the first and second portions causing a displacement ofat least a portion of the actuator, which actuator displacement doesmechanical work without the need to be coupled to a structure which doessaid work.

The present invention also relates to actuator systems constructed andarranged to be displaced from a first orientation to a secondorientation comprising at least one electrochemical cell comprising anegative electrode and a positive electrode, wherein one or both of thenegative and positive electrodes is an actuator, and comprises a firstportion and a second portion, and wherein upon charge and/or discharge,a species is intercalated, de-intercalated, or alloys with the firstportion to a different extent than the second portion, and experiences aresulting dimensional change relative to the second portion, therebyimparting to the actuator a differential strain between the first andsecond portions causing a displacement of at least a portion of theactuator, which actuator displacement does mechanical work without theneed to be coupled to a structure which does said work.

The present invention also relates to actuator systems constructed andarranged to be displaced from a first orientation to a secondorientation comprising at least one electrochemical cell comprising anegative electrode and a positive electrode, wherein one or both of thenegative and positive electrodes is an actuator, and comprises a firstportion and a second portion, and wherein upon oxidation and/orreduction of the first portion to a different extent than the secondportion, and experiences a resulting dimensional change relative to thesecond portion, thereby imparting to the actuator a differential strainbetween the first and second portions causing a displacement of at leasta portion of the actuator, which actuator displacement does mechanicalwork without the need to be coupled to a structure which does said work.

The present invention also relates to actuator systems constructed andarranged to be displaced from a first orientation to a secondorientation comprising at least one electrochemical cell comprising anegative electrode and a positive electrode, wherein one or both of thenegative and positive electrodes is an actuator, and comprises a firstportion and a second portion, and wherein upon charge and/or discharge,a species is electrochemically deposited at the first portion to adifferent extent than the second portion, and experiences a resultingdimensional change relative to the second portion, thereby imparting tothe actuator a differential strain between the first and second portionscausing a displacement of at least a portion of the actuator, whichactuator displacement does mechanical work without the need to becoupled to a structure which does said work.

The present invention also relates to actuator devices comprising atleast one electrochemical cell comprising a negative electrode, apositive electrode, and a species that can intercalate, de-intercalate,alloy with, oxidize, reduce, or plate with a first portion of theelectrochemical cell to an extent different than a second portion of theelectrochemical cell, the first and/or second portions therebyundergoing a dimensional change upon discharge causing actuatordisplacement which does mechanical work, wherein the electrochemicalcell is constructed and arranged to be charged in manufacture, and ispartially discharged after use or is not further charged after firstdischarge.

The present invention also relates to infusion pumps comprising at leastone electrochemical cell comprising a negative electrode, a positiveelectrode, and an intercalation species, wherein the negative and/orpositive electrode undergoes a dimensional change upon charge and/ordischarge so as to cause infusion of a fluid into a body.

The present invention also relates to actuators constructed and arrangedto be used in a physiological setting, the actuators comprising a firstportion adjacent a second portion, wherein the first portion undergoes adimensional change upon exposure to a bodily fluid comprising a species,and wherein resulting electrochemical intercalation of the species intothe first portion, de-intercalation of the species from the firstportion, or oxidation/reduction of the first portion as a result ofcontact with the species, imparts a dimensional change of the actuator.

The present invention also relates to electrochemical actuators foradministering a drug into a body, the electrochemical actuatorscomprising at least one negative electrode, at least one positiveelectrode, and a species, wherein the electrochemical actuator issubjected to an applied voltage or current, whereby application of thevoltage or current or cessation thereof includes intercalation of thespecies in at least one electrode of the electrochemical actuator,resulting in a volumetric or dimensional change of the electrochemicalactuator, and wherein the volumetric or dimensional change results inadministration of a drug into a body.

The present invention also relates to actuator systems constructed andarranged to be displaced from a first orientation to a secondorientation comprising at least one electrochemical cell comprising anegative electrode and a positive electrode, wherein one or both of thenegative and positive electrodes is an actuator and comprises a firstportion and a second portion, the first and second portions arrangedsuch that the electrode has at least a two-fold symmetry when viewednormal to a surface of the electrode, and wherein upon charge and/ordischarge, a species is intercalated, de-intercalated, alloys with,oxidizes, reduces, or plates with the first portion to a differentextent than the second portion, and experiences a resulting dimensionalchange relative to the second portion, thereby imparting to the actuatora differential strain between the first and second portions causing adisplacement of at least a portion of the actuator.

The present invention also relates to actuator systems constructed andarranged to be displaced from a first orientation to a secondorientation comprising at least one electrochemical cell comprising asubstantially planar electrode and a substantially planarcounterelectrode; and a separator in contact with the electrode andcounterelectrode, wherein the electrode and counterelectrode arearranged such that the electrode comprises a first surface positioned toreceive a species from the counterelectrode, and a second, opposingsurface positioned to receive the species from the counterelectrode to alesser extent, relative to the first surface, the second surfacecomprising a nonreactive metal or polymer, and wherein, upon chargeand/or discharge, the species is intercalated, de-intercalated, alloyswith, oxidizes, reduces, or plates with the first surface to a greaterextent than the second surface, and the electrochemical cell undergoes adimensional change so as to cause a displacement of at least a portionof the actuator.

The present invention also provides methods for fabricating actuators.In some embodiments, the method comprises fabricating at least fiveactuators, each actuator comprising a negative electrode and a positiveelectrode, wherein one or both of the negative and positive electrodesis an actuator, and comprises a first portion and a second portion, suchthat, upon charge and/or discharge, a species is intercalated,de-intercalated, alloys with, oxidizes, reduces, or plates with thefirst portion to a different extent than the second portion, andexperiences a resulting dimensional change relative to the secondportion, thereby imparting to the actuator a differential strain betweenthe first and second portions causing a change in orientation of atleast a portion of the actuator, wherein each of the at least fiveactuators undergoes substantially the same change in orientation, underessentially the same conditions.

In some embodiments, the method comprises fabricating an actuator, eachactuator comprising a negative electrode and a positive electrode,wherein one or both of the negative and positive electrodes is anactuator, and comprises a first portion and a second portion, such that,upon charge and/or discharge, a species is intercalated,de-intercalated, alloys with, oxidizes, reduces, or plates with thefirst portion to a different extent than the second portion, andexperiences a resulting dimensional change relative to the secondportion, thereby imparting to the actuator a differential strain betweenthe first and second portions causing a change in orientation of atleast a portion of the actuator, wherein the actuator undergoessubstantially the same change in orientation over at least 10charge/discharge cycles of the actuator.

Any of the foregoing embodiments may be constructed and arranged to beused in a physiological setting, including the administration of a druginto a body or as an infusion pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of an actuator system (a) without application ofa voltage or current and (b) with application of a voltage or current,according to one embodiment of the invention.

FIG. 2 shows an example of an actuator system (a) without application ofa voltage or current and (b) with application of a voltage or current,for dispensing a fluid in an adjacent fluid container, according to oneembodiment of the invention.

FIGS. 3A-C show an actuator system having sufficient stiffness to affectthe rate of displacement and the stroke length of the actuator.

FIG. 4 shows an example of an actuator system, according to oneembodiment of the invention.

FIG. 5 shows another example of an actuator system, according to oneembodiment of the invention.

FIG. 6 shows another example of an actuator system, according to oneembodiment of the invention.

FIG. 7 shows another example of an actuator system, according to oneembodiment of the invention.

FIG. 8A shows an actuator system comprising first and second portionsbeing formed of different materials.

FIG. 8B shows an actuator system comprising first and second portionsbeing formed of different materials, after immersion in water.

FIG. 9 shows an actuator system comprising a Zn layer (a) in Zn form and(b) upon conversion of Zn to Zn(OH)₂, resulting in actuation of theactuator system.

FIG. 10 shows another actuator system comprising a Zn layer (a) in Znform and (b) upon conversion of Zn to Zn(OH)₂, resulting in actuation ofthe actuator system.

FIG. 11 shows an actuator system comprising a lithium ion couple,wherein the actuator (a) is at zero strain before exposure to anelectrolyte and (b) undergoes actuation after exposure to theelectrolyte.

FIG. 12 shows a lithium ion couple or a nickel metal-hydride coupleassembled in (a) the charge state and (b) upon spontaneous dischargeafter emergence in an electrolyte.

FIG. 13 shows an actuator system comprising two different portions (a)prior to exposure to an electrolyte and (b) upon exposure to anelectrolyte, wherein the system undergoes bending or cupping.

FIG. 14 shows an actuator system comprising two different portions (a)prior to exposure to an electrolyte and (b) upon exposure to anelectrolyte, wherein the system undergoes bending or opening of thestructure.

FIG. 15 shows an actuator system having a hinged structure (a) prior toexposure to a species and (b) upon exposure to a species, wherein thesystem undergoes actuation.

FIG. 16 shows a schematic design for a self-powered electrochemicalpump.

FIG. 17 shows a graph of displacement versus time curve for self-poweredmorphing actuator with built-in strain amplification.

FIG. 18 shows a graph of the displacement curve for an electrochemicalmorphing actuator controlled by a 20% duty cycle.

FIG. 19 shows a galvanostatic discharge profile of a bimorphelectrochemical actuator utilizing a 0.10 mm thick tin foil bonded tocopper foil.

FIG. 20 shows a galvanostatic discharge profile of an electrochemicalbimorph cell utilizing a 0.05 mm thick tin foil bonded to copper.

FIG. 21A shows a photograph of the top side of a 1-inch square plate tinelectrode actuator after discharge, wherein the device shows a ½ inchlithium disc negative electrode positioned on the tin plate and thelarge deformation of the actuator.

FIG. 21B shows a photograph of the back side of the tin electrode in(a), showing large deformation.

FIG. 21C shows a graph of the displacement versus discharge capacity ofthe actuator for a 1-inch square tin plate electrode as described inExample 11 and the ½-inch diameter tin disc electrodes as described inExample 10.

FIG. 22 shows (a) a photograph of a folded actuator with no externalload and (b) a photograph of an actuator, wherein suppression of foldingmotion occurs with the application of an external load to produce aradially symmetric actuator.

FIG. 23 shows a photograph of a three-fold symmetric electrode for useas an electrochemical actuator.

FIG. 24 shows a graph of the displacement and current versus time duringdischarge for a three-fold symmetric electrode actuator.

FIG. 25 shows a photograph of a three-fold symmetric tin electrodeactuator, after discharge.

FIG. 26 shows examples of actuators having a various modes ofdisplacement.

FIG. 27 shows a photograph of a masked, ¾-inch diameter aluminum disc,with a ¼ inch wide strip of exposed aluminum across the diameter of thedisc.

FIG. 28 shows a photograph of a packaged electrochemical actuator, uponfolding.

FIG. 29 shows a graph of the displacement of disc-shaped aluminumactuators upon discharge, as a function of time, where displacement isshown to be nearly linear with time.

Other aspects, embodiments and features of the invention will becomeapparent from the following detailed description when considered inconjunction with the accompanying drawings. The accompanying figures areschematic and are not intended to be drawn to scale. For purposes ofclarity, not every component is labeled in every figure, nor is everycomponent of each embodiment of the invention shown where illustrationis not necessary to allow those of ordinary skill in the art tounderstand the invention. All patent applications and patentsincorporated herein by reference are incorporated by reference in theirentirety. In case of conflict, the present specification, includingdefinitions, will control.

DETAILED DESCRIPTION

The present invention generally provides systems and devices involvingelectrochemical actuation, and related methods.

In some cases, the present invention provides systems (e.g., actuatorsystems) that may comprise at least one component, wherein applicationof a voltage or current to the component may generate a volumetric ordimensional change of the component. In some cases, the volumetric ordimensional change may produce mechanical work. In some embodiments, atleast a portion of the system may be constructed and arranged to bedisplaced from one orientation to another orientation. The system mayalso be associated with another structure, such that a volumetric ordimensional change of the system may affect the orientation, shape,size, volume, or other characteristic, of the structure. Systems such asthese may be useful in various applications, including pumps (e.g.,infusion pumps) and drug delivery devices, for example.

In some embodiments, the system may comprise a species associated withone or more components (e.g., electrodes) during operation of thesystem. The species, such as an ion, may be capable of interacting withone or more portions of the device. Some embodiments of the inventionmay involve interaction of a species with one or more electrodes of thedevice, generating a volumetric or dimensional change in the electrode.As used herein, a “volumetric or dimensional change” refers to theexpansion, contraction, and/or other displacement of a system or portionof a system. The volumetric or dimensional change may comprise one ormore amounts of expansion, contraction, elongation, shortening,twisting, bending, shearing, or other displacement in one or moredimensions. In some cases, the volumetric or dimensional change may beisotropic. In some cases, the volumetric or dimensional change may beanisotropic. Such changes may be employed for mechanical work, i.e.,actuation. The systems may undergo any range of volumetric ordimensional changes that may be suitable for a particular application.For example, an actuator system may be positioned in contact with afluid container and may expand and contract such that the system servesas a pumping device to dispense fluid from the fluid container.

In some embodiments, the present invention provides an electrochemicalactuator comprising at least one electrochemical cell including ananode, a cathode, and a species (e.g., lithium ion), wherein theelectrochemical cell undergoes a volumetric or dimensional change uponthe application of a voltage or current. In some embodiments, theelectrochemical actuator also comprises a structure including at leastone portion constructed and arranged to be displaced from a firstorientation to a second orientation, e.g., by the volumetric ordimensional change of the one, or plurality of electrochemical cells. Asthe portion of the structure is displaced, mechanical work is produced.As discussed in more detail below, a variety of systems can be actuatedby the volumetric or dimensional change of an electrochemical cell.

As used herein, an actuator system “constructed and arranged to bedisplaced” refers to an actuator system that may alter the orientationof the system, i.e., through displacement (e.g., actuation) of at leasta portion of the system, which affects the performance of the system orstructure associated with the system in its intended purpose. Those ofordinary skill in the art would understand the meaning of this term. Inan illustrative embodiment, an actuator system may be positionedadjacent a structure such as a fluid container or reservoir, wherein theactuator system is constructed and arranged such that motion or otherdisplacement of the system affects the position, shape, size, or othercharacteristic of the fluid container to pump or dispense fluid from thefluid container.

Advantageously, displacement of a system, or a portion of a system, froma first orientation to a second orientation can be achieved through avariety of methods, e.g., bending, cupping, twisting, elongating, andcontracting, which can be altered by, for example, varying the materialcomposition of the system, the configuration of one or moreelectrochemical cells of the system, the voltage or current applied, theduty cycle, or other operating parameters, as described more fullybelow. In cases where the system is associated with a structure,displacement of the system may be altered by, for example, changing thepositioning of the electrochemical cell in relation to the structure tobe displaced, the shape of the structure, any materials in operativerelationship between the cell and the structure, and/or the materialcompositions of the components. In some cases, the displacement maycomprise a linear displacement of a portion of the system. In somecases, the displacement may comprise cupping of a portion of the system.For example, the system may comprise a disk-shaped portion that may havea first, planar orientation, and, upon actuation, the disk-shapedportion may be displaced via cupping to a nonplanar, hemispherical,second orientation.

The method by which the system, or portion thereof, is displaced can betailored to suit a particular application. In some cases, actuators andmethods described herein may advantageously provide the ability toreproducibly produce actuators that can undergo a particular, desiredchange in orientation. That is, actuators and methods of the inventionmay allow for the fabrication of at least five actuators, wherein eachof the at least five actuators may undergo substantially the same changein orientation, under essentially the same conditions (e.g., electricfield). In some cases, at least 10, at least 25, at least 50, at least100, at least 250, at least 500 actuators, or greater, may be fabricatedsuch that each actuator may undergo substantially the same change inorientation, under essentially the same conditions.

In some cases, actuators and methods described herein may produce anindividual actuator that may undergo substantially the same change inorientation over multiple charge/discharge cycles. That is, the actuatormay reproduce substantially the same change in orientation over at least10, at least 100, at least 500, or greater, charge/discharge cycles ofthe actuator. As used herein, changes in orientation that are“substantially the same” may be changes in orientation that differ byless than 10%, less than 5%, or, in some cases, less than 1%, of theaverage displacement of the actuator and/or of the average rate ofdisplacement of the actuator.

For example, methods of the invention may involve selecting one or moreappropriate materials for use as electrodes and/or arranging the variousmaterials with respect to one another to produce a desired change inorientation (e.g., a desired bending, buckling, folding, cupping). Insome embodiments, an electrode may be selected to have a particularshape, thickness, or other dimension and may be arranged to produce adesired displacement. The size, shape, and/or arrangement of thematerials may affect the method and degree of the change in orientation.In some cases, an electrode may have one or more exposed portionsarranged such that an electrochemical reaction may take place at theexposed portions, while un-exposed portions (e.g., “masked” portions)may undergo an electrochemical reaction to a different, or lesser,degree, under essentially the same conditions.

In some embodiments, a device (e.g., actuator) comprises a monolithicelectrode such as a metal plate or sheet, wherein the product of anelectrochemical charge or discharge reaction may form a layer on atleast a portion of the surface of the monolithic electrode. This mayresult in a differential strain, which causes bending, cupping, folding,or other changes in orientation, of the actuator. In some cases, theactuator may be self-amplifying since a large absolute displacement ofthe actuator can be obtained for a small extent of reaction of theelectrode.

As noted above, the cross-sectional shape, thickness, or other dimensionof the electrode(s) may be selected to obtain a particular mode ofdisplacement (e.g., deformation) of the actuator. In some embodiments,the mode of displacement may be modulated via incorporation of one ormore displacement-guiding features within the electrode, such as groovesor exposed portions that undergo a electrochemical reaction to adifferent degree than other portions of the electrode. For example, anelectrode in the shape of a circular disc may deform uponelectrochemical reaction to form a “cupped” shape that has approximatelythe shape of a spherical cap. In some cases, an electrode in the shapeof a square plate may deform upon electrochemical reaction into a“cupped” shape that deviates from a spherical cap by having four-foldsymmetry when viewed normal to the face of the plate. In some cases, anelectrode (e.g., a disc-shaped electrode or a square-shaped electrode)may be induced to undergo a mechanical instability that results infolding of the electrode, so that the actuator has two-fold symmetrywhen viewed normal to the face of the actuator. In some embodiments, arectangular electrode may preferentially fold upon actuation along anaxis that is parallel to the short direction of the electrode. In somecases, an electrode sheet that initially has three-fold symmetry (e.g.,a disc-shape) may form a cupped shape with three-fold symmetry. Forexample, a “tripod” configuration may be formed, which provides theadvantage that the three “legs” of the tripod define a plane and allowthe three-fold symmetry actuator to bear uniformly against a supportingsurface.

FIG. 26 shows some illustrative embodiments of actuators arranged suchthat a particular method of displacement may occur upon electrochemicalreaction. FIG. 26A shows a disc-shaped electrode 402 having portions 400which may be exposed such that portion 400 undergoes an electrochemicalreaction to a greater extent than unexposed portions of electrode 402.In operation, portions 402 may react (e.g., may be lithiated orde-lithiated) to produce displacement of electrode 402 into a cuppedconfiguration. FIG. 26B shows another embodiment, wherein disc-shapedelectrode 406 includes various grooves 404 positioned about 120°relative to one another, such that electrode 406 bends along grooves 404upon reaction. FIG. 26C shows a square electrode 410 having a portion408 which may be exposed such that portion 408 undergoes anelectrochemical reaction to a greater extent than unexposed portions ofelectrode 410. In operation, portion 408 may react to producedisplacement of electrode 410 into a cupped shape.

FIG. 26D shows another embodiment, wherein a square-shaped electrode 414includes an exposed portion 412 at which an electrochemical reactionprimarily occurs, relative unexposed portions of electrode 414.Displacement of electrode 414 may occur based on the deformation ofexposed portion 412. In another embodiment, the mode of deformation of abar or rod of electrode material may be controlled by varying thecross-sectional shape and absolute dimensions of the bar. In oneinstance, a bar of rectangular cross-section has a thickness to widthratio, t/w, and length, 1, that is greater than t or w. Theelectrochemical reaction may occur primarily at the surface defined by wand 1. The mode of deformation of the bar can be selected by varying theratio t/w. For t/w<<1, the dominant mode of deformation may be a bendingor folding of the bar about the long axis of the bar, namely the axisparallel to the length, 1. For t/w closer to unity or greater thanunity, the mode of deformation may be selected to be a bending of thebar along an axis parallel to w and normal to the length direction, 1.

In some embodiments, the electrode may be “masked” to select (e.g.,limit) the regions of the electrode that may undergo electrochemicalreaction to a different (e.g., greater, lesser) extent than theremaining portions of the electrode. In some cases, the electrode may bein a form including but not limited to a plate, sheet, disc, or bar thatis formed from a monolithic material such as a solid metal. Theelectrode may, in some cases, be formed from a porous material includingpressed or sintered powders. The electrode may be masked by theapplication or deposition of a non-reactive surface layer or surfacelayers forming a reaction barrier, such that the masked areas of theelectrode undergo an electrochemical reaction to a lesser or toessentially no degree, while the exposed or unmasked areas of theelectrode may undergo the electrochemical reaction to a greater degree,under essentially the same conditions. In some embodiments, the unmaskedareas of the electrode may undergo an electrochemical reaction to alesser or to essentially no degree, while the masked areas of theelectrode may undergo the electrochemical reaction to a greater degree,under essentially the same conditions. This may cause the electrode todeform to a controlled and predetermined geometry providing advantagessuch as controlled deformation symmetry or rate of deformation or extentof strain amplification, as shown in several examples herein.

In some embodiments, the masking material is a nonreactive metal orpolymer. In some embodiments, the metal is copper or nickel. In someembodiments, the masking material is applied to a surface of theelectrode by evaporation, sputtering, chemical vapor deposition,dip-coating, spray-coating, or other methods of depositing a thincoating known to those skilled in the art. In some embodiments, themasking material is applied as an adhesive sheet or tape, for example asa copper metal tape or Kapton® polymer tape.

In some embodiments, the primary area of reaction of the electrode maybe the center of a plate or sheet electrode, such that greater strainamplification may be obtained and unreacted regions may act as “legs” orlevers to amplify the total displacement of the actuator.

In some embodiments the actuator comprises two substantially planarelectrodes (e.g., an electrode and a counterelectrode) separated by andin contact with a separator, wherein a surface of the electrode thatfaces away from the counterelectrode may be masked or plated to limit orprevent electrochemical reaction. This may allow for the electrochemicalreaction to occur primarily on the unmasked portions of the electrode,i.e., the surface of the electrode that faces the counter electrode.

In some embodiments, controlled deformation is obtained by applying apattern of electrochemically active material to a substrate thatundergoes limited or essentially no electrochemical reaction while theactuator is in operation. In one embodiment, the pattern may be appliedby masking the substrate to restrict the areas of deposition while thereactive material is applied. The pattern of electrochemically activematerial may be selected to obtain a desired mode of deformation asdescribed in previous embodiments.

Additionally, the degree of displacement of a structure, or a portion ofa structure, can be tailored towards the particular application. Forexample, in some embodiments, electrochemical cells of the invention cancause displacement of a structure, or a portion of a structure, of,e.g., greater than 5 degrees, greater than 10 degrees, greater than 20degrees, greater than 30 degrees, or greater than 40 degrees. Dependingon the particular application, in other embodiments, electrochemicalcells can cause displacement of, e.g., greater than 1 cm, greater than10 cm, greater than 20 cm, greater than 50 cm, or greater than 1 m.

In some cases, the volumetric or dimensional displacement of anelectrochemical cell upon charging or discharging may be used to carryout a physical displacement of the system, a portion of the system, or astructure adjacent or otherwise associated with the system. Thevolumetric or dimensional displacement (e.g., net volume change) may bepositive, zero, or negative during charge and/or discharge. In somecases, the net volume change and may be readily computed from the volumechanges occurring in each of the constituent materials using tabulateddata for the molar volumes of the constituent materials of the cell as afunction of their composition or state-of-charge, or measured directlyon the electrochemical cell.

Several different structures can be actuated by an electrochemical celldescribed herein. In some embodiments, the invention provides actuatorsystems (e.g., electrochemical actuators) constructed and arranged to bedisplaced from first orientation to a second orientation, upon charge ordischarge. In some cases, the actuator system may be constructed andarranged to be altered from a first shape to a second shape, upon chargeor discharge. In some cases, the displacement produced by the actuatormay have the same sign (e.g., positive, negative) as the volumetric ordimensional change occurring in the electrochemical cell. For example, apositive displacement (e.g., increase in a linear dimension) maycorrespond to a positive net volume change (e.g., expansion) of theelectrochemical cell itself, and a negative displacement (decrease in alinear dimension) may correspond to a negative net volume change(contraction) of the electrochemical cell itself. In some cases, thedisplacement produced by the actuator may not have the same sign as thevolumetric or dimensional change occurring in the electrochemical cell.For example, as described in the Examples, a positive displacement maybe produced by an electrochemical cell undergoing a net negative volumechange. That is, the displacement of the actuator may be decoupled fromthe volumetric or dimensional change of the electrochemical cell.

The actuator system can include at least one electrochemical cellcomprising a negative electrode and a positive electrode. The actuatorsystem may also include, for example, greater than or equal to 2,greater than or equal to 4, greater than or equal to 10, greater than orequal to 20, or greater than or equal to 50 electrochemical cells thatcan be operated in series or parallel. In some embodiments, multipleelectrochemical cells may be joined in parallel electrically but may bestacked in order to increase overall displacement while maintaining alow overall device voltage. In some embodiments the net volume change ofthe electrochemical actuator is used to perform a physical displacementresulting in the pumping or dispensing of a fluid, or the administrationof a fluid to a body, including but not limited to a fluid comprising adrug.

In some embodiments, one or both of the negative and positive electrodesmay be an actuator and can change shape and/or be displaced from a firstorientation to a second orientation, upon charge or discharge of theelectrochemical cell. In some cases, the actuator system can comprise afirst portion and a second portion, optionally in electricalcommunication with one another, wherein the first portion and a secondportion undergo a differential volumetric or dimensional change, ordifferential displacement, upon charge or discharge. For example, theelectrode(s) undergoing shape change or displacement may comprise afirst portion that imposes a mechanical constraint on a second portionthat may facilitate displacement of the electrode(s). In someembodiments a first portion is in electrical communication with a secondportion. In some embodiments a first portion is not in electricalcommunication with a second portion.

In some instances, a first portion and a second portion (e.g.,corresponding to positive and negative electrodes, respectively or viceversa, of the electrochemical cell) maybe in the form of layers, whichmay be positioned immediately adjacent one another, or in otherembodiments, can be separated from one another by another material. Insome embodiments, the first and second portions are bonded to oneanother. In some embodiments, the first and second portions aredifferent regions of the same part of the system, wherein one portionundergoes electrochemically induced volumetric or dimensional change toa greater extent than the other.

In some embodiments, upon charge and/or discharge, a species (e.g., anintercalation species, an electron, or a plating species) intercalates,de-intercalates, alloys with, oxidizes, reduces, or plates with or intothe first portion to a different extent (e.g., to a different degree,concentration, strain, volume, shape change, or other change) than thesecond portion. For example, the species may substantially intercalate,de-intercalate, or alloy with, oxidize, reduce, or plate the firstportion, but not with the second portion, or with the second portion toa lesser extent than the first portion. As a result of the differentialintercalation, de-intercalation, or alloying, oxidation, reduction, orplating of the first portion to a different extent than the secondportion, the first portion may experience a resulting dimensionalchange, such as an increase or decrease in volume or a linear dimensionor a change in aspect ratio. Because the second portion does notintercalate, de-intercalate, or alloy with, oxidize, reduce, or platethe species, or does so to a lesser extent than the first portion, thesecond portion may not undergo a substantial dimensional change, or maynot undergo the same dimensional change as the first portion. As aresult, a differential strain (e.g., an opposing strain) is impartedbetween the first and second portions, which can cause a displacement(e.g., internal flexure or bending) of at least a portion of theactuator. The resulting displacement of the actuator can do mechanicalwork without the need to be coupled to a structure which does said work.In certain embodiments of the invention, actuation of an actuator caninclude expansion, contraction, bending, bowing, cupping, folding,rolling, or other forms of displacement from a first orientation to asecond orientation.

In some cases, the actuator system may itself be a strain-amplifying orstrain-deamplifying structure. For example, the actuator system, orportion thereof (e.g., an electrode), may amplify any displacementarising from, for example, a volume change that occurs in the system, orportion thereof. In some embodiments, the actuator system or device mayamplify displacement arising from a volumetric change of an electrode.Displacement of the actuator may be used to exert a force or to carryout a displacement of a structure adjacent the actuator.

For any of the actuator systems and devices (e.g., pumps) describedherein, while displacement of the actuator system, or portion thereof,can be used to perform mechanical work without the need to be coupled toa structure which does said work, in some cases, the actuator system maybe coupled to a structure which does mechanical work (e.g., astrain-amplifying structure, a strain de-amplifying structure). In somecases, the actuator system may not be coupled to a structure which doesmechanical work.

An example of an actuator system is shown in the embodiment illustratedin FIG. 1A. As shown in this illustrative embodiment, actuator system110 includes a negative electrode 112 in electrical communication withpositive electrode 114. Positive electrode 114 may include a firstportion 116 and a second portion 118. In some embodiments, portions 116and 118 are formed of different materials. Portions 116 and 118 may alsohave different electrical potentials. For example, portion 116 maycomprise a material that can intercalate, de-intercalate, alloy with,oxidize, reduce, or plate a species to a different extent than portion118. Portion 118 may be formed of a material that does not substantiallyintercalate, de-intercalate, or alloy with, oxidize, reduce, or platethe species. In some cases, portion 116 may be formed of a materialcomprising one or more of aluminum, antimony, bismuth, carbon, gallium,silicon, silver, tin, zinc, or other materials which can expand uponintercalation or alloying or compound formation with lithium. In oneparticular embodiment, portion 116 is formed of a material comprisingaluminum, which can expand upon intercalation with lithium. Portion 118may be formed of copper, since copper does not substantially intercalateor alloy with lithium. In some instances, portion 118 may act as apositive electrode current collector, and may extend outside theelectrochemical cell, e.g., to form a tab or current lead. In otherembodiments, portion 118 may be joined to a tab or current lead thatextends outside the cell. Negative electrode 112 may also include acurrent collector. Actuator system 110 may include separator 122. Theseparator may be, for example, a porous separator film, such as a glassfiber cloth, or a porous polymer separator. Other types of separators,such as those used in the construction of lithium ion batteries, mayalso be used. The actuator may also include electrolyte 124, which maybe in the form of a liquid, solid, or a gel. The electrolyte may containan electrochemically active species, such as that used to form thenegative electrode. Actuator system 110 may be sealed an enclosure 126,such as a polymer packaging.

As illustrated in the embodiment shown in FIG. 1B, the electrochemicalcell may have a voltage 132, such that, when a closed circuit is formedbetween the negative and positive electrodes, an electronic current mayflow between the two electrodes through the external circuit. Ifnegative electrode 112 is a lithium metal electrode and the electrolytecontains lithium ions, lithium ion current can flow internally fromelectrode 112 to electrode 114. The intercalation of portion 116 withlithium can result in a dimensional change, such as a volume expansion.In some instances, this volume expansion may reach at least 25%, atleast 50%, at least 75%, at least 100%, at least 150%, at least 200%, atleast 250%, or at least 300% compared to the initial volume. High volumeexpansion may occur, for example, when portion 116 is saturated withlithium. As portion 116 increases in volume due to intercalation oflithium, portion 118 to which portion 116 may be bonded, may notsubstantially expand due to minimal or no intercalation of lithium.Portion 116 thus provides a mechanical constraint. This differentialstrain between the two portions causes positive electrode 114 to undergobending or flexure. As a result of the dimensional change anddisplacement of the positive electrode, actuator system 110 can bedisplaced from a first orientation to a second orientation. Thisdisplacement can occur whether the volumetric or dimensional change(e.g., net volume change) of the electrochemical cell, due to the lossof lithium metal from the negative electrode and formation of lithiumintercalated compound or lithium alloy at the positive electrode, ispositive, zero, or negative. In some cases, the to actuator displacementmay occur with a volumetric or dimensional change (e.g., net volumechange) of the actuator system, or portion thereof, that is positive. Insome cases, the actuator displacement may occur with a volumetric ordimensional change (e.g., net volume change) of the actuator system, orportion thereof, that is zero. In some cases, the actuator displacementmay occur with a volumetric or dimensional change (e.g., net volumechange) of the actuator system, or portion thereof, that is negative.

As used herein, “differential strain” between two portions refers to thedifference in response (e.g., actuation) of each individual portion uponapplication of a voltage or current to the two portions. That is, asystem as described herein may include a component comprising a firstportion and a second portion associated with (e.g., may contact, may beintegrally connected to) the first portion, wherein, under essentiallyidentical conditions, the first portion may undergo a volumetric ordimensional change and the second portion does not undergo a volumetricor dimensional change, producing strain between the first and secondportions. The differential strain may cause the component, or a portionthereof, to be displaced from a first orientation to a secondorientation. In some cases, the differential strain may be produced bydifferential intercalation, de-intercalation, alloying, oxidation,reduction, or plating of a species with one or more portions of theactuator system.

For example, the differential intercalation, de-intercalation, alloying,oxidation, reduction, or plating of portion 116 relative to portion 118can be accomplished through several means. (FIG. 1A) In one embodiment,as described above, portion 116 may be formed of a different materialthan portion 118, wherein one of the materials substantiallyintercalates, de-intercalates, alloys with, oxidizes, reduces, or platesa species, while the second portion interacts with the species to alesser extent. In another embodiment, portion 116 and portion 118 may beformed of the same material. For example, portion 116 and portion 118may be formed of the same material and may be substantially dense, orporous, such as a pressed or sintered powder or foam structure. In somecases, to produce a differential strain upon operation of theelectrochemical cell, portion 116 or 118 may have sufficient thicknesssuch that, during operation of the electrochemical cell, a gradient incomposition may arise due to limited ion transport, producing adifferential strain. In some embodiments, one portion or an area of oneportion may be preferentially exposed to the species relative to thesecond portion or area of the second portion. In other instances,shielding or masking of one portion relative to the other portion canresult in lesser or greater intercalation, de-intercalation, or alloyingwith the masked or shielded portion compared to the non-masked orshielded portion. This may be accomplished, for example, by a surfacetreatment or a deposited barrier layer, lamination with a barrier layermaterial, or chemically or thermally treating the surface of the portionto be masked/shielded to either facilitate or inhibit intercalation,de-intercalation, alloying, oxidation, reduction, or plating with theportion. Barrier layers can be formed of any suitable material, whichmay include polymers, metals, or ceramics. In some cases, the barrierlayer can also serve another function in the electrochemical cell, suchas being a current collector. The barrier layer may be uniformlydeposited onto the surface in some embodiments. In other cases, thebarrier layer may form a gradient in composition and/or dimension suchthat only certain portions of the surface preferentially facilitate orinhibit intercalation, de-intercalation, alloying, oxidation, reduction,or plating of the surface. Linear, step, exponential, and othergradients are possible. In some embodiments a variation in the porosityacross portion 116 or 118, including the preparation of a dense surfacelayer, may be used to assist in the creation of an ion concentrationgradient and differential strain. The invention also contemplates othermethods of interaction of a species with a first portion to a differentextent so as to induce a differential strain between the first andsecond portions. In some embodiments, the flexure or bending of anelectrode is used to exert a force or to carry out a displacement thataccomplishes useful function, as described in more detail below.

In several embodiments described herein, the first and second portionsmay be described as being formed of different materials, resulting indifferent characteristics and properties. It should be understood that,for any embodiments described herein, the first portion and the secondportion may also be formed of substantially the same material. In caseswhere the first portion and the second portion may be formed of the samematerial, the first and second portions may optionally have at least onediffering characteristic, such as dimension, thickness, porosity, or thelike, which may produce differential intercalation, de-intercalation,alloying, oxidation, reduction, or plating, resulting in differentialstrain. For example, the first and second portions may comprise the samematerial but may have different porosities, resulting in a porositygradient along the first and second portions. In some cases, the firstportion may comprise a porous material (e.g., powder compact, foam)having a first density, and the second portion may comprise the porousmaterial having a second density different than the first density.

As described herein, some embodiments of the invention involveinteraction of a species with one or more electrodes. For example, theelectrode(s) may be intercalated with the species. In some embodiments,during operation of the actuator system or device, one electrode mayobtain a spatially-varying concentration of the species, resulting in adifferential strain, producing displacement of at least a portion of thesystem or device. That is, the species may be, for example, intercalatedinto one portion of the electrode to a greater extent than into a secondportion of the electrode, resulting in differential strain.

Actuators of the invention, or portions thereof (e.g., electrodes),especially those that include at least a first portion that canintercalate, de-intercalate, alloy with, oxidize, reduce, or plate aspecies to a different extent than a second portion, can have anysuitable shape such as a plate, sheet, strip, folded sheet or strip,beam, cup, rod, tube, cylinder, etc., so long as it can be displacedfrom a first orientation to a second orientation, which can be used foraccomplishing a desired function. In some cases, at least a portion ofthe actuator may perforated, and/or may have multiple “legs” or “arms”or branches. In some cases, the positive and/or negative electrode isnonplanar. For example, the positive and/or negative electrode can be aplate or pellet, or other nonplanar shape. In some embodiments, thepositive and/or negative electrode may have any shape and may comprisesat least one groove, wherein the groove(s) may facilitate and/or guidedisplacement of the actuator system, or portion thereof. For example, anelectrode may be grooved or embossed so as to facilitate, guide, ordirect the manner in which the electrode is moved from a firstorientation to a second orientation. In some cases, the electrode mayfold along at least one groove upon actuation.

Actuators of the invention can range in size from the nanometer scale,to the micrometer scale, and to the macroscopic scale. For example, insome embodiments, actuator system 110 may have at least one dimensionless than or equal to 1 meter, less than or equal to 10 centimeters,less than or equal to 1 centimeter, less than or equal to 1 millimeter,less than or equal to 100 microns, less than or equal to 10 microns,less than or equal to 1 micron, less than or equal to 100 nanometers, orless than or equal to 10 nanometers.

An electrode of an actuator can also range in size from the nanometerscale, to the micrometer scale, and to the macroscopic scale. Forexample in some embodiments, electrode 114 may have at least onedimension less than or equal to 1 meter, less than or equal to 10centimeters, less than or equal to 1 centimeter, less than or equal to 1millimeter, less than or equal to 100 microns, less than or equal to 10microns, less than or equal to 1 micron, less than or equal to 100nanometers, or less than or equal to 10 nanometers.

Actuators (including electrodes) that include a first portion that canintercalate, de-intercalate, alloys with, oxidize, reduce, or plate witha species to a different extent than a second portion may be formed ofany suitable material in any suitable form that allows interaction withsaid species (e.g., a dimensionally-active material). In someembodiments, the first portion is formed of a porous material thatchanges dimension upon ion exchange. The change in dimension may be arelatively uniform volume expansion or contraction, or may be a flexureor bending or cupping mode of deformation resulting from introduction ofdifferential strain, as described herein. The porous material may be apressed powder compact or metal foam or composite of thedimensionally-active material. The second portion may be formed of anon-dimensionally active material. The first and second portions mayoptionally comprise additives such as a binder or conductive additivesuch as carbon or a metal. The dimensionally-active material maycomprise, for example, one or more of the following species: Al, Au, Ag,Ga, Si, Ge, Ti, Sn, Sb, Pb, Zn, carbon, graphite, hard carbon,mesoporous carbon, an oxide, intercalation oxide, layered oxide, claymineral, sulfide, layered sulfide, TiS₂, MoS₂, and WS₂. It should beunderstood that actuators of the invention may also comprise othermetals, metal-containing compounds, inorganic materials, and the like.

In some cases, actuators of the invention may undergo a dimensionalchange provided by a porous electrode that changes dimension upon ionexchange. In some cases, the porous electrode, upon charge or discharge,undergoes a dimension change comprising bending, flexing, or cupping. Insome embodiments, the porous electrode may comprise a porosity gradient,wherein a first portion of the porous electrode has a porosity that isdifferent than the porosity of a second portion of the porous electrode.In some cases, the porous electrode further comprises a surface layer incontact with the porous electrode, wherein the surface layer isintercalated, de-intercalated, alloyed with, oxidized, reduced, orplated to a greater extent than the (underlying) porous electrode. Thesurface layer may partially or substantially cover or encapsulate theouter surface of the porous electrode, such that the surface layer maybe primarily and/or directly exposed to other components of the system.In some cases, the surface layer may be intercalated or alloyed to agreater extent than the underlying porous electrode. In some cases, thesurface layer may have a higher density then the underlying porouselectrode.

In some cases, a species that can intercalate, de-intercalate, alloyedwith, oxidize, reduce, or plate at least a portion of an actuator (e.g.,a portion of an electrode) may be in the form of an ion. Non-limitingexamples of ions include a proton, hydroxide ion, sulfate ion, chlorateion, phosphate ion, and a nitrate ion. In other cases, the species maycomprise an alkali metal or an alkaline earth metal. In certainembodiments, the species is an electron, which can cause oxidation orreduction of at least a portion of a surface. In other embodiments, thespecies is a plating species, which can be electrochemically depositedat the first portion to a different extent than the second portion. Insome cases, the species may be selected from the group consisting of aproton, alkali ion, lithium, ion complex, hydroxyl ion, carbonate ion,chlorate ion, sulfate ion, phosphate ion, other multi-atomic ioncomplexes, and the like. In some cases, the species is selected from thegroup consisting of a proton, alkali ion, ion complex, hydroxyl ion,carbonate ion, chlorate ion, sulfate ion, and phosphate ion. In somecases, the species is a proton.

The species may be initially present in an electrochemical cell in theform of a solid, such as the material used to form the active species ofthe positive or negative electrodes. In other cases, the species may bein the form of a solid that is laminated to one of the electrodes, butis not a part of the active material of the electrode. In anotherembodiment, the species may be in the form of a separate solid ionsource, such as a solid electrolyte. In yet another embodiment, thespecies may be present in the form of a liquid or a gel, e.g., as anelectrolyte, and may be present in the electrochemical cell before firstcharge/discharge of the cell. In other embodiments, these species may bepresent in a substance exterior to the electrochemical cell. Forinstance, the species may be present in the environment in which theactuator is used. In one particular embodiment, the actuator is designedto be immersed in a fluid containing a species that can intercalate,alloy with, oxidize, reduce, or plate a portion of an electrode of theelectrochemical cell. For example, the fluid may be a bodily fluid andthe species may be an ionic species present in the bodily fluid.

In some cases, a device of the invention may comprise an anode, cathode,and lithium ions as the species. Upon application of an electric fieldbetween the anode and the cathode, the device may be reversibly chargedand discharged. In some cases, upon charging, the lithium ions mayinsert into the anode such that the anode undergoes a volumetric ordimensional change relative to the cathode, which remains essentiallyunchanged in volume or dimension. Upon discharging, the lithium ions maybe transported from the anode to the cathode such that the lithium ionsare inserted into the cathode. As a result, the anode may return to itsvolume/shape prior to charging, and the cathode may undergo a volumetricor dimensional change relative to the anode. In some cases, both theanode and cathode, either simultaneously or non-simultaneously, mayundergo a volumetric or dimensional change upon charge/dischargecycling. In some cases, only one of the anode and cathode may undergo avolumetric or dimensional change upon charge/discharge cycling.

Actuators of the invention can be used in a variety of applications. Forexample, actuators can be used in microfluidic devices, in which, forexample, switching and valving functions can be performed by theactuator. In other cases, the actuator may be used as a pump to causefluid flow in a channel or out of an orifice, including a pump for thecontrolled delivery of a drug. In other embodiments, an actuator can bepart of an external or implantable medical device. The species that mayintercalate, de-intercalate, oxidize, reduce, or plate with at least aportion of the actuator (e.g., a portion of an electrode) may be part ofthe electrochemical cell in some embodiments (e.g., in manufacturebefore being used); however, in other embodiments may be a constituentof the environment in which the actuator is used. Actuators may also bepart of micro electro mechanical systems (MEMS) devices such asmicromirror arrays in which addressable micro actuators are individuallyactuated. In other cases, one or more actuators can be constructed andarraigned to unfold into a structure upon application of a current orvoltage. Such structures may be useful as tents or scaffolds, forexample. In other cases, an actuator of the invention can be a componentof a surgical tool or medical implant that can be electrically expandedor contracted by an electrical input. A variety of applications aredescribed in more detail below.

In some embodiments, actuators of the invention may be used to displaceor deform a structure adjacent the actuator. For example, as shown inthe embodiment illustrated in FIG. 2A, actuator system 150 includesactuator 151 that serves as a pump to dispense fluid 170 from reservoir172. The pump may dispense different volumes of fluids, for example,greater than 0.01 mL, greater than 0.01 mL, greater than 1 mL, greaterthan 5 mL, greater than 10 mL, greater than 100 mL, greater than 1 L.Actuator 151 may operate in a similar manner to actuator 110 describedin FIG. 1. Briefly, a species may intercalate, de-intercalate, alloy,oxidize, reduce, or plate with first portion 156 of electrode 154 in anon-uniform manner relative to portion 158, such that a differentialstrain is induced between the first and second portions. The secondportion may be a mechanical restraint, which causes flexure or bendingof electrode 154, and resultantly, flexure or bending of actuator 151.Reservoir 172 adjacent actuator 151 may be formed of a deformablematerial such that flexure of actuator 151 causes an increase inpressure inside the reservoir, forcing fluid 170 to be dispensed fromthe reservoir, as shown in FIG. 2B. In some embodiments, the rate ofdispensing or infusion of fluid 170 from the reservoir can be controlledby the rate and/or extent of displacement (e.g., stroke length) of theactuator from a first position to a second position. The rate ofdispensing may be controlled such that is constant or variable. The rateand/or extent of actuation may be controlled by parameters such as theamplitude and/or duration of the applied current or voltage (e.g.,during charge or discharge), concentration of species to beintercalated, de-intercalated, alloyed, or plated with an electrode ofthe electrochemical cell, and the dimensions and material compositionsof the materials used to form the electrochemical cell, such as theconfiguration and material compositions of the first and second portionsof the actuator, which interact with the species to different extents.

One or more electrochemical cells may be arranged, optionally incombination with one or more components, to achieve displacement of asystem, or a portion of a system. In some cases, electrochemical cellshaving different actuation abilities may be arranged on a surface in apattern, wherein each electrochemical cell is independently controlled.Other configurations of cells, components, and/or devices may be used inthe context of the invention, as described in, for example, U.S. PatentPublication No. 2006/0102455, which is based on U.S. patent applicationSer. No. 11/150,477, and International Publication No. WO2005/124918,which is based on International Application Ser. No. PCT/US/2005/020554,both of which are incorporated herein by reference.

Actuators of the invention can be fabricated with different stiffness ofmaterials to allow for different ranges of actuation rate and strokelength. For example, an actuator having a long stroke length may beformed of one or more materials having a relatively low stiffness. Insuch an embodiment, a short pulse of current can cause slow displacementof an actuator from a first orientation to a second orientation. Incontrast, an actuator formed of one or more stiffer materials may bedisplaced only when current is applied. In such an embodiment, theactuator can be displaced from a first orientation to a second or thirdorientation with each increment of applied current, in some instances,without regard to the load. In some embodiments, the transfer of energyfrom the actuator to a mechanical system is maximized when the stiffnessof the actuator and the mechanical systems are matched. Accordingly, thechoice of materials of the actuator can be chosen based on theparticular application and/or the mode of actuation desired.

FIGS. 3A-C show an example of how the stiffness of an actuator caninfluence the rate of displacement and the stroke length of theactuator. In the embodiment illustrated in FIG. 3A actuator 180 includesa first portion that can intercalate, de-intercalate, alloy with,oxidize, reduce, or plate a species to an extent different than a secondportion. End 181 of the actuator may be fixed in a position, with theactuator in a first position α. The actuator may be adjacent a piston190 and reservoir 192 containing fluid 194. Upon non-uniformintercalation, de-intercalation alloying, oxidation, reduction, orplating of a species (e.g., with the first portion with respect to thesecond portion of the actuator), actuator 180 may be displaced fromposition α to position c, as shown in FIG. 3C. Actuator 180 may beformed of one or more materials having a low stiffness to achieve a longstroke length “αc”. This may be achieved, for example, by applying ashort pulse of current to the actuator such that the actuator isdisplaced, which can cause displacement of piston 190, to dispense thefluid from the reservoir. A short pulse of current may slowly push thefluid out of the reservoir until the actuator relaxes to its newequilibrium position c. In contrast, FIG. 3B shows actuator 182 formedof a high stiffness material in a first orientation, where an end of theactuator is at position b. Upon application of a current of similarmagnitude and duration as that to actuator 180, actuator 182 may bedisplaced from position b to position c, as shown in FIG. 3C. The strokelength of actuator 182, “bc,” is shorter than the stroke length ofactuator 180, “αc,” due to the different stiffness of the materials usedto form actuators 180 and 182. In some embodiments, actuators can bestacked, e.g., either in parallel or in series, to increase the load orforce applied to a structure.

The following examples further illustrate different configurations andways in which actuators of the invention can be implemented.

In the embodiment illustrated in FIG. 4, actuator system 200 includesactuator 210 including positive electrode 212, negative electrode 214,and electrolyte layer 216 including species 218 that can intercalate,de-intercalate, alloy with, oxidize, reduce, or plate with the positiveor negative electrode. The transport of the species through theelectrolyte layer under applied voltage 220 can be used to displaceactuator 210 up or down in the directions of arrows 222 and 224. Thisdisplacement can result in actuation that, for example, can be used toopen or close a valve, displace a mirror, pump, fluid, etc. As discussedabove, the combinations of materials used to form the positive andnegative electrodes can vary. For instance, suitable materials mayinclude the active materials in a lithium ion or nickel-metal hydridebattery. As illustrated in this embodiment, actuator system 210 is fixedat one end to substrate 228. The substrate can act as a mechanicalconstraint such that portion 230 of the actuator undergoes minimal or nodisplacement. Because portion 232 of the actuator is not fixed, thisportion undergoes displacement which results in bending.

In another embodiment, the species that can intercalate, alloy with,oxidize, reduce, or plate with a portion of an actuator can bepositioned such that one portion of the actuator is preferentiallyexposed to the species, while a different portion of the actuator isnon-exposed, or exposed to the species to a lesser extent. For example,in the embodiment illustrated in FIG. 5, actuator system 250 includesactuator 252 comprising portion 254 and portion 256. Portion 256 may beexposed to species 260, which is immersed in substance 262 (e.g., anelectrolyte) to a greater extent than portion 254. Portion 254 andsubstrate 264 may be conductive and serve as the positive and negativeelectrodes. Portion 256 may be insulated from substrate 264 by insulator266. Upon application of a potential difference between the substrate(or a remote counter electrode) and portion 254, species 260 mayintercalate, de-intercalate, alloy with, oxidize, reduce, or plateportion 256 to an extent greater than portion 254. The type ofinteraction of portions 254 and/or 256 with species 260 will depend on,for example, the particular type of species, and the materials used toform portions 254 and 256. This interaction can cause flexure ofactuator 252 as a result of the differential strain between portions 254and 256.

Structures such as actuator systems 200 and 250 may be fabricated by awide o variety of methods including MEMS fabrication, various method ofdeposition of thin film structures, thick film coating technology,electrode deposition methods, and physical assembly and lamination.Other methods of fabrication may also be suitable and are known to thoseof ordinary skill in the art.

As shown in the embodiment illustrated in FIG. 6, actuator system 270includes electrode 272 in electrical communication with actuator 276,which may be integrally connected (or non-integrally connected) tosubstrate 274. Actuator 276 may be uniform in composition; however,portion 280 may be exposed to species 282 to a larger extent thanportion 284 of the actuator. Different exposure (e.g., different areasof exposure) to the species can cause intercalation, de-intercalation,alloying, oxidation, reduction, or plating with portion 280 to adifferent extent than portion 284. This can cause actuation of theactuator, e.g., in the direction of arrows 222 and 224.

In some embodiments, actuators of the invention are constructed andarranged to be used in a physiological setting, such as within a body.For example, some embodiments of the invention provide electrochemicalactuators for administering a drug into a body, comprising at least onenegative electrode, at least one positive electrode, and a species asdescribed herein, wherein the electrochemical actuator may be subjectedto an applied voltage or current, whereby application of the voltage orcurrent or cessation thereof includes intercalation of the species in atleast one electrode of the electrochemical actuator, resulting in avolumetric or dimensional change of the electrochemical actuator. Insome cases, the volumetric or dimensional change may be useful in theadministration of a drug into a body, or a fluid comprising a drug intoa body, for example, via dispensing or infusing methods, and othermethods, as described herein.

In some instances, the actuator is immersed a bodily fluid (e.g., blood,urine, sweat, etc.) comprising a species that can intercalate with aportion of an electrode of the actuator. Upon intercalation, theelectrode may undergo displacement from a first orientation to a secondorientation. In other embodiments, species may de-intercalate from aportion of the electrode into the body upon exposure to the bodilyfluid. Or in other embodiments, the species may oxidize or reduce aportion of the electrode upon exposure to the bodily fluid, which canresult in displacement. In other instances, the actuator may be usedoutside of the body, for example, the actuator may be exposed to abodily fluid removed from a body.

FIG. 7 is an illustrative example of an actuator that can be used in aphysiological setting. Actuator 290 includes positive electrode 292,negative electrode 294, and insulator 296 positioned between the twoelectrodes. Actuator 290 may be immersed in bodily fluid 298 comprisingspecies 299, which can intercalate into or de-intercalate out of oneelectrode to a greater extent than the other electrode, for instance,upon application of a voltage or current. This can cause displacement ofthe actuator from a first orientation to a second orientation. Differentmodes of displacement of the actuator can be achieved depending on themechanical design of the actuator. For example, the actuator may be inthe shape of a beam, accordion, stent, disc, or a multi-layered stackedstructure. Other shapes and designs of actuators can also be used so asto induce expansion, contraction, folding, twisting, bending, rolling,etc. of the structure from a first orientation to a second orientation.In some embodiments, the actuator may be in the form of a medicalimplant or a component of an implant, such as a stent, sensor,prosthetic, and the like.

In another embodiment of the invention, an actuator system includes atleast one electrochemical cell comprising a negative electrode, apositive electrode, and a species that can intercalate, de-intercalate,alloy with, oxidize, reduce, or plate with a first portion of theelectrochemical cell to an extent different than a second portion of theelectrochemical cell. As a result of one of the interactions above ofthe species with the first and/or second portion, the first and/orsecond portions may undergo a dimensional change upon discharge, causingactuator displacement which does mechanical work. In some embodiments,the electrochemical cell is constructed and arranged to be charged inmanufacture, and discharged during use. In some embodiments, theelectrochemical cell is constructed and arranged to be charged inmanufacture, and is partially discharged after use, or, is not furthercharged after first discharge. The actuator system may be constructedand arranged to spontaneously discharge. In some cases, the actuator maybe discharged one or more times at different instances to cause severalactuations. Upon discharge (e.g., partial discharge, completedischarge), the actuator may be disposed. Such a configuration may beuseful for portable devices such as certain pumps, sensors, implants,and medical devices.

One embodiment of the invention includes an infusion pump for infusing afluid into a body. The infusion pump includes at least oneelectrochemical cell comprising a negative electrode, a positiveelectrode, and a species, wherein the negative and/or positive electrodeundergoes a dimensional change upon charge and/or discharge so as tocause infusion of the fluid into the body. Alternatively, the infusionpump may not include a species in manufacture, but upon exposure to aspecies during use, the infusion pump can perform actuation and infuse afluid. In some arrangements, the infusion pump is constructed andarranged to spontaneously discharge. Such a device is self-powered,meaning the electrochemical cell of the device is fabricated in thecharged state. The device can include positive and negative electrodematerials selected such that the electrochemical cell expands or deformsupon discharging. For example, low cost materials such as silicon andtin can be used as expanding materials (e.g., by as much as 300%) uponbeing lithiated.

The pumping rate, including the magnitude of volume dispensed and theduration of dispensing, can be determined by the cell expansion ordeformation rate, which can in turn be controlled through the dischargerate of the electrochemical cell. Control of discharge can be performedby various methods such as by varying the resistance of an externalcircuit through which the cell discharges. External controls caninclude, for example, a resistor, including a thin metal or wire thatalso serves as a fuse. This can be used to permit controlledself-discharge of the electrochemical cell through the resistor orexternal circuit. In a particular embodiment, a variable-resistor isimplemented in the external circuit, including a solid-state circuit, inorder to control the discharge rate and pumping rate. By varying theexternal resistance of the cell, the instantaneous discharge rate andactuation rate can be controlled.

In another embodiment, the duty cycle of the device may be varied inorder to control the extent or degree of displacement or pumping. Inthis embodiment, the external circuit through which the devicedischarges or charges may be repeatedly switched between open- andclose-circuit, or “on and off.” That is, the duty cycle may becontrolled by opening and/or closing an external circuit associated withthe actuator device. The frequency and duration of the on/off pulses canprovide control of the rate of displacement and total displacement. Forexample, if a device under external short-circuit conditions exhibitscomplete discharge in time t resulting in total strain ε, switchingbetween open- and closed-circuit conditions such that the total timespent in closed-circuit is t/10 corresponds to a 10% duty cycle, withthe net strain being ε/10. In embodiments where the duration of theclosed-circuit pulse is constant, the rate of deformation can becontrolled by varying the pulse frequency. The pulse frequency andduration can also be independently varied to accommodate inherentnonlinearities in the displacement vs. time response of the device inorder to achieve a desired displacement vs. time profile of the actuatoror pump.

In other embodiments, the rate of discharge can be designed into thecell (e.g., a self-discharge rate can be engineered). In one particularembodiment, the internal impedance of the cell is designed, usingmethods known to those skilled in the art of electrochemical devices orbatteries, in order to produce a desired rate of discharge. Underexternal short-circuit conditions, or those conditions where theresistance between the external leads of the cell is substantially lowerthan the cell internal impedance, the rate of discharge and thereforethe rate of actuation is primarily determined by the internal impedanceof the cell. For example, the cell may be designed for a certain maximumrate of discharge and lower rates introduced using the control methodsdescribed herein, or may be designed to have a relatively high internalimpedance providing a safe, low rate of discharge even under accidentalshort-circuit conditions.

Rate and/or amount of device deformation (and corresponding rate and/oramount of pumping of a pump controlled by such a device) can be builtinto the device such that, for example, a one-use disposable devicepumps at a predetermined, set rate and time and/or volume. Alternativelyor in addition, a device can be constructed with a control so that rateand/or extent of discharge/pumping can be varied during use of thedevice or set among one of several different settings prior to use ofthe device. In some instances, where a device can be used multipletimes, rate and/or amount of discharge/pumping can be varied betweenuses, during uses, etc. Those of ordinary skill in the art are well ableto design, through digital or analog circuitry or a combination, systemsin a device for any of these features.

Through these and/or other means, the pumping rate can be varied widelyby controlling the discharge rate of the electrochemical cell. In someembodiments, the discharge rate can be remotely controlled, for example,wirelessly through transmission signals sent to a control circuit thatcontrols the duty cycle or resistance of the external load. The pump maydispense different volumes of fluids, for example, greater than 0.01 mL,greater than 0.1 mL, greater than 1 mL, greater than 5 mL, greater than10 mL, or greater than 50 mL, if desired.

Applications of actuators of the invention in the form of a pump can beused for applications including, but not limited to, subcutaneousdelivery of drugs or fluids, intravenous, intrathecal, and other commonmethods of drugs and fluid delivery to the body, air fresheners orperfume dispensers, and implantable drug delivery devices.

For example, it is well-known that when a bimetal couple is immersed inan electrolyte, one of the bimetal pair is the anode and ispreferentially not oxidized while the other is preferentially oxidized.An example is the anodic protection of iron and steel with zinc. In anillustrative embodiment, FIG. 8A shows a first portion 302 and a secondportion 304, the first and second portions being formed of differentmaterials. FIG. 8B shows the same structure after immersion in water.The structure now includes layer 306. If the first portion comprises Fe,the second portion comprising Zn, upon exposure to water, portion 306 isformed, comprising Zn(OH)₂. The reaction at portion 302 is 2H⁺+2e=H₂(g)and the reaction at portion 306 is Zn+2(OH⁻)=Zn(OH)₂+2e.

As shown FIGS. 9A-B, actuator 310 includes first portion 312 and secondportion 314. If the first portion is formed of Fe and the second portion314 is formed of Zn in thin layers, upon conversion of Zn to Zn(OH)₂,the volumetric expansion during formation of Zn(OH)₂ (e.g.,Zn+2(OH⁻)=Zn(OH)₂+2e) would result in spontaneous actuation, causingdisplacement in the form of bending, as shown in FIG. 9B. Thisspontaneous actuation can be harnessed in actuators of the invention toperform mechanical work.

As shown in FIG. 10A-B, if first portion 320 is formed of Zn and thesecond portion 322 is formed of Fe, upon conversion of Zn (e.g.,Zn+2(OH⁻)=Zn(OH)₂+2e), the structure 318 will open, as shown in FIG.10B. This type of actuation would be useful for structures such as astent, an expanding disk to relieve a compressive stress betweenvertebrate, or other structures. Similar types of actuation can beaccomplished using a species that simply swells by preferentialabsorption of an ion or a molecular species from a fluid.

Those of ordinary skill in art would be able to select other bimetalpairs that would be suitable for use in the invention.

In the body, it is desirable to avoid significant gas evolution. It isalso desirable to have ductile yet strong materials that undergopermanent plastic deformation, for certain applications. In someembodiments, it may be advantageous to use an actuator thatspontaneously discharges when a positive and negative material areelectrically shorted to each other and immersed in an electrolytecontaining a species that can intercalate, de-intercalate, alloy with,oxidize, reduce, or plate with at least a portion of the actuator.

FIGS. 11A-B show a lithium ion couple (e.g., one portion comprisingLi_(0.5)CoO₂ and another portion comprising Li_(x)Ti₅O₁₂, where x>4)assembled in the charge state and which undergoes spontaneous dischargeupon emergence in an electrolyte. (Alternatively to a lithium ioncouple, the actuator may be a nickel metal-hydride couple (e.g., oneportion comprising Ni³⁺OOH and the other portion comprising MH_(x),where M is a metal), assembled in the charge state and which undergoesspontaneous discharge upon emergence in an electrolyte.) FIG. 11A showsthe actuator at zero strain before exposure to an electrolyte and FIG.11B shows the actuator after exposure to the electrolyte. Upondischarge, a first portion of the actuator expands to a larger volumethan a second portion of the actuator, thereby causing bending(contraction) of the actuator. Thus, the spontaneous discharge uponexposure of the actuator to an electrolyte can cause actuation.

FIGS. 12A-B show a lithium ion couple or a nickel metal-hydride coupleassembled in the charge state (FIG. 12A) and which undergoes spontaneousdischarge (FIG. 12B) upon emergence in an electrolyte. The shape of theactuator causes it to expand upon spontaneous discharge.

Several types of materials can be used in actuators of the invention.For example, titanium metal may be used as an electrode material whenthe species is hydrogen, since titanium metal is a very good hydrogenabsorption medium. Other suitable hydrogen absorption media includenoble metals. Pt, Rh, Ir and Au are also ductile and strong metals thatcan be used as electrode materials. In one particular embodiment, aspontaneously-opening stent (or other actuator design) can be fabricatedby joining, for example, a hydrated metal to a non-hydrated metal suchthat upon exposure to an electrolyte, the transfer of hydrogen from oneto the other causes displacement of the actuator. This specific approachcan also benefit from the introduction of a diffusion barrier betweenthe two metals, as is widely used in semiconductor device technology, toavoid diffusion of hydrogen between the two metals causing actuationbefore exposure to the electrolyte, as shown in FIGS. 13-14. FIG. 13shows an actuator system comprising two different portions, eachcomprising a different material (e.g., metal), and optionally adiffusion barrier positioned between each portion, (a) prior to exposureto an electrolyte and (b) upon exposure to an electrolyte, wherein thesystem undergoes bending or cupping. Similarly, FIG. 14 shows anactuator system comprising two different portions, each comprising adifferent material (e.g., metal), and optionally a diffusion barrierpositioned between each portion, (a) prior to exposure to an electrolyteand (b) upon exposure to an electrolyte, wherein the system undergoesbending or opening of the structure. In some embodiments, iridium isattractive as a metal used to form at least a portion of the actuatordue to its biocompatibility.

In another embodiment, actuators of the invention can include hingedstructures, e.g., as shown in FIGS. 15A-B. The actuator may includefirst portion 342 that can preferentially intercalate, de-intercalate,alloy with, oxidize, reduce, or plate a species, and second portion 344that does not preferentially intercalate, de-intercalate, alloy with,oxidize, reduce, or plate the species. In some instances, second portion346 and third portion 348 are formed of the same material. Upon exposureof the actuator to a first species, the first portion can intercalate,de-intercalate, alloy with, oxidize, reduce, or plate a species to adifferent extent than that of the first and/or third portion, causingdisplacement (e.g., expansion) of the actuator, as shown in FIG. 15B.Optionally, second portion 346 and third portion 348 are formed ofdifferent materials, and upon exposure to a second species, the actuatormay be displaced from a first orientation to a second orientation.

Actuators of the invention including a first portion and a secondportion, which upon charge and/or discharge, a species is intercalated,de-intercalated, alloys with, oxidizes, reduces, or plates with thefirst portion to an extent different than the second portion, the firstportion experiencing a resulting dimensional change relative to thesecond portion, can be used in a variety of settings. Accordingly,actuators of the invention can have configurations, shapes, and/ordesigns, other than those described above. Examples, of suchconfigurations shapes, and/or designs include those described in U.S.Pat. Nos. 6,545,384; 5,907,211; 5,954,079; 5,866,971; 5,671,905; and5,747,915, which are each incorporated herein by reference.

Considerations for the design of low voltage, long-life electrochemicalactuators are now described. In some embodiments, the design of a lowvoltage, long-life electrochemical actuator includes certain operatingcriteria. In one embodiment, a method of operating an electrochemicalcell comprising a negative electrode, a positive electrode, a nonaqueouselectrolyte, and lithium as a species (e.g., an intercalation species)is provided. The electrochemical cell can be operated such that thepositive electrode has an average equilibrium potential (or open-circuitvoltage (OCV)) with respect to metallic lithium over the state of chargeof its use that is less than about +4V. The negative electrode can havean average potential with respect to metallic lithium over the state ofcharge of its use that is greater than about +0.2V. The electrochemicalcell may be in operative relationship with a component that can bedisplaced from a first orientation to a second orientation. Operation ofthe electrochemical cell can cause a volumetric or dimensional change ofthe electrochemical cell. Upon application of a voltage of less thanabout 10V to the electrochemical cell, the component can be displacedfrom the first orientation to the second orientation from the volumetricor dimensional change of the electrochemical cell.

As described in more detail below, too high of a potential at thepositive electrode can result in electrochemical corrosion of thecurrent collector and/or active materials at the positive electrode. Insome cases, the high potential can also cause degradation of nonaqueouselectrolytes or salts, which can result in loss of electrolyteconductivity and/or undesirable side effects within the cell. As such,certain electrochemical cells of the invention can be operated to havean average equilibrium potential over the state-of-charge of the cell ofless than about +4V, less than about +3.5V, less than about +3.0V orless than about +2.5V.

Also described below, too low of an average equilibrium potential (e.g.,with respect to metallic lithium over the state of charge of its use)can cause negative affects such as electrochemical corrosion of thenegative electrode current collector or the deposition of lithium metal.Accordingly, electrochemical cells may be operated such that thenegative electrode has an average equilibrium potential of greater thanabout +0.2V, greater than about +0.5V, greater than about +1.0V, orgreater than about +1.5V. Depending on the particular electrochemicalcell, a maximum and a minimum range of average equilibrium potential ofthe positive and negative electrodes, respectively, can be chosen. Forinstance, in one embodiment, the positive electrode has an averageequilibrium potential of less than about +3.5V and the negativeelectrode has an average equilibrium potential of greater than about+0.5V. In another embodiment, the positive electrode has an averageequilibrium potential of less than about +3.5V and the negativeelectrode has an average equilibrium potential of greater than about+1.0V. In yet another embodiment, the positive electrode has an averageequilibrium potential of less than about +3.5V and the negativeelectrode has an average equilibrium potential of greater than about+1.5V. In yet another embodiment, the positive electrode has an averageequilibrium potential of less than about +3.0V and the negativeelectrode has an average equilibrium potential of greater than about+0.5V. Of course, other ranges of average equilibrium potential for thepositive and negative electrodes can be chosen.

In certain embodiments, operating an electrochemical cell can involveapplying a voltage of less than about 10V to the electrochemical celland, from the volumetric or dimensional change of the electrochemicalcell, displacing the component from a first orientation to a secondorientation. As discussed in more detail below, the applied voltage(i.e., the operating voltage) is generally low so as to increase thecycle life of the electrochemical actuator. Accordingly, operating anelectrochemical cell may include applying a voltage of less than about10V, less than about 8V, less than about 7.5V, less than about 6V, lessthan about 5V, or less than about 4V. It should be understood, however,that for certain periods requiring high power actuation over short timedurations, applied voltages may be higher than the steady-state voltageapplied. Accordingly, greater than 95% of the operating life of anelectrochemical cell may be operated with an applied voltage of lessthan about 10V, less than about 8V, less than about 7.5V, less thanabout 6V, less than about 5V, or less than about 4V. In other instances,greater than 90%, greater than 80%, greater than 70%, greater than 60%,or greater than 50% of the operating life of the electrochemical cellmay be operated at such voltages.

The following considerations for the design of low voltage, long-lifeelectrochemical actuators are described specifically for the design ofnonaqueous electrolyte lithium electrochemical cells. However, is shouldbe understood that the principals can also be applied to anyelectrochemical cell used as an actuator.

The driving force for transport of a species, including an ionicspecies, in an electrochemical cell used as an actuator can be theoverpotential (during charging) or underpotential (during discharging),the overpotential and underpotential being, respectively, the magnitudeof the applied voltage over and under the equilibrium or rest oropen-circuit voltage (OCV) of the cell at a particular state of charge.The OCV as a function of state of charge can be readily determined bythose of ordinary skill in the art if the potential vs. x(concentration) of each compound is known, and if cell parameters suchas the ratio of cathode to anode material and the degree of irreversibleloss of the ionic species during cycling are known. For example,LiCoO₂-graphite cells can have an OCV that varies continuously withstate of charge between about 3.9V and about 3V, while LiFePO₄-graphitecells have a nearly constant voltage of about 3.3V over a wide state ofcharge.

For high rate of actuation, it may be desirable to have a largeoverpotential during charge and large underpotential during discharge.On the other hand, it is also recognized herein that the range ofpotentials applied to an electrochemical cell can influence theperformance and life of the cell, especially over many charge/dischargecycles, for several reasons. At the high end of the operating voltagerange, it is recognized that too high a potential can causeelectrochemical corrosion of the current collector (such as aluminum) oractive materials at the positive electrode, or degradation of nonaqeuouselectrolytes or salts. This can result in loss of electrolyteconductivity or undesirable side effects such as formation of gas withinthe cell. At the low end of the operating voltage, too low a potentialcan cause electrochemical corrosion of the negative electrode currentcollector (such as copper) or the deposition of lithium metal, thelatter occurring if the potential at the negative electrode reaches thatat which metallic lithium is stable. Thus, for high rate of actuation,as well as for stability and long life in a nonaqueous lithiumelectrochemical cell used for actuation, it may be desirable to have arelatively low OCV such that a high overpotential can be applied duringcharge without reaching stability limits of the electrolyte system orpositive current collector. However, the low OCV should not be too low;otherwise, a high underpotential applied during discharge may reachpotentials at which anode current collectors (such as copper) dissolve,or this may cause metallic lithium may be plated. The selection ofactive materials for the positive and negative electrodes meeting thesecriteria is important, as it may be desirable to provide high actuationenergy and power in electrochemical cells of the invention.

In some embodiments, it is desirable to have a positive electrodematerial with both high rate and high strain, and an OCV measured withrespect to metallic lithium that is less than about 4V. In otherembodiments, the OCV measured with respect to lithium is less than about3.5V, less than about 3V, or less than about 2.5V. Non-limiting examplesof such positive electrode materials include electrode compounds basedon LiFePO₄, TiS₂, TaS₂, and their alloys and compositionally modifiedforms. In some cases, electrochemical cells include negative electrodematerials with high power as well as an OCV over the range ofcomposition used that is at least +0.1 V with respect to metalliclithium. In other cases, the OCV is at least +0.5V or more. For example,graphite can be a suitable material when used with a positive electrodematerial such that the net strain is substantial. Another suitablematerial includes Li_(x)TiO₂ spinel, e.g., the starting compositionLi₄Ti₅O₁₂, which upon lithiation has a nearly constant potential ofabout 1.57V with respect to metallic lithium over a wide range oflithium compositions and nearly zero volume change. Accordingly, thiscan allow the volume change at the positive electrode to be used foractuation. In some embodiments, electrochemical cells based on suchcombinations of positive and negative electrode materials have cell OCVstypically less than about 3.5V. Of course, it is possible to have a cellvoltage that varies between positive and negative values as the cell ischarged or discharged, while maintaining throughout the above describedconditions of a positive electrode potential that is not too high and anegative electrode potential that is not too low with respect tometallic lithium.

When such a cell is used for electrochemical actuation, theoverpotential and underpotential applied can result in a chargingvoltage that is above, and a discharging voltage that is below, the cellOCV. However, generally, the absolute value of the operating voltage ofthe cell remains low. For example, the absolute value of the operatingvoltage may be less than about 10V, less than 7.5V, less than 5V, orless than about 3.5V. It should be noted that for high power actuationover short time duration, the applied voltages can be of a pulsed natureand can safely be significantly higher than the steady-state voltagethat would normally result in electrochemical damage to such cells.However, for operation of electrochemical cells under conditions wherethe cell's voltage is maintained, to obtain long life, the appliedvoltage may result in a potential at the positive electrode that is lessthan about 5V, less than about 4.5V, or less than 4V, with respect tometallic lithium. This can be permitted by the use of positive electrodematerials based on compounds such as LiFePO₄, LiTiS₂, and LiTaS₂.

Selection criteria for high mechanical energy density, high powerelectrochemical actuation compounds are now described. The theoreticalmechanical energy density of actuation compounds is given by theequation ½ Eε², where E is the elastic modulus and ε is the strain thatcan be induced under particular operating conditions. Thus, materials ofhigh strain and high elastic modulus have the potential for providinghigher energy density in electrochemical cells of the invention.

With respect to electrochemical actuators, it is recognized herein thatthe strain obtained is not necessarily linear with the concentration ofintercalating or alloying species in the electrochemical cell. Forexample, in a graph of the strain vs. Li concentration x of theintercalation compound LixTiS₂, the slope of the curve is steepest atlow Li concentrations, as described in U.S. patent application Ser. No.11,796,138, incorporated herein by reference. Accordingly, it isdesirable when using LixTiS₂ as an electrochemical actuation compound,to operate over a range of x of about 0 to 0.4 if it is desirable toobtain the most mechanical energy for a given electrical energy used tooperate the actuator, and/or to obtain the highest mechanical power fromthe actuator. The latter follows from the consideration that the amountof intercalated species x is the product of the electrical current andtime, so that for a particular operating current, faster actuation isobtained for compounds with a higher strain for a given value of x.

It is also recognized that the mechanical power of electrochemicalactuators may depend on the rate capability (e.g., rate of charge ordischarge) of the electrochemical cell. High rate capability may beobtained by selecting electrolytes of high ionic conductivity and/ordesigning cells so that the ion or electron diffusion lengths are short.For a particle-based electrode, for example, a fine particle size may bedesirable in order to decrease the diffusion length, and accordingly,the diffusion time.

The transport properties of materials can be, therefore, also animportant selection criterion for designing electrochemical actuators.For example, the chemical diffusion coefficient of the ionic speciesresponsible for the volume change may be selected to be high. Oneembodiment of the invention identifies a “power factor” that can be usedas a figure of merit for comparing different materials, given by theequation ½ Eε²D, where D is the chemical diffusion coefficient of theionic species in the material of interest. FIG. 4 compares the powerfactor of different materials against their specific gravity. It isnoted that materials of high power factor and low specific gravity pcan, all else being equal, provide higher specific power as anelectrochemical actuator. For example, layered dichalcogenides such asTiS₂ and TaS₂ may be particularly useful electrochemical actuationcompounds according to these criteria.

The inventors have recognized that figures of merit of interest in thefield of actuation also include power density, which is the mechanicalpower available per unit volume, and specific power, which is themechanical power available per unit mass. It is desirable to maximizethe values of both in most actuation applications. It should be notedthat the power density of electrochemical actuators requiresconsideration of the characteristic diffusion length that the ionicspecies are transported over during operation of the electrochemicalactuator. While the transport length includes the length betweenelectrodes, through the porosity of the electrode, and across theseparator, the rate of actuation does not exceed the time necessary fordiffusional transport into the material itself. Thus, both the particlesize (for a particle-based actuator) and the chemical diffusioncoefficient are important factors. To compare materials on a equalbasis, assuming that materials can be processed to have similar particlesizes, the power density can be defined as the quantity ½(Eε²D_(Li)/x²), and the specific power as ½ (Eε²x²ρ/D_(Li), where x isthe particle dimension (e.g., radius or diameter). FIG. 4 compares thepower density of different materials against their specific gravity, andFIG. 6 compares the power density against the specific power ofdifferent materials. From these selection criterion, suitable materialsfor electrochemical actuators can be chosen. For example, layereddichalcogenides such as TiS₂ and TaS₂ can be particularly usefulelectrochemical actuation compounds.

In one embodiment, electrochemical actuators of the invention utilize atleast two (e.g., a first and a second) electrochemical actuators workingin concert such that as one is charged (e.g., in order to produce usefulmechanical work), the other is discharged, or vice versa. For example, asystem or device may comprise a first and a second electrochemical cellconfigured in an antagonistic arrangement relative to one another, suchthat discharge of the first cell results in charging of the second cell,and discharge of the second cell results in charging of the first cell.The article may also include a component constructed and arranged to bedisplaced from a first orientation to a second orientation by chargeand/or discharge of at least one of the first and second electrochemicalcells. Of course, a structure including electrochemical cells that areconfigured in an antagonistic arrangement relative to one another caninclude a plurality of such sets of electrochemical cells, e.g., greaterthan 2, greater than 5, greater than 10, greater than 20 or greater than50 pairs of electrochemical cells that are configured in an antagonisticarrangement. Such cells can be operated in series or in parallelrelative to one another. Although pairs of opposed actuators have beenused in active structures previously (for the reason that most actuatorswork better in tension than in compression or vice versa), there areadditional benefits of such designs for use in the electrochemicalactuators of the invention. Electrochemical actuators store or releaseelectrical energy at the same time that they are performing mechanicalwork, and if such electrical energy is dissipated (e.g., in the form ofheat by dissipating the electrical energy through a resistor), theenergy consumption of the actuator or system of actuators can be high.However, by shuttling electrical energy between actuators so that as oneis charged the other is discharged, electrical energy is largelyconserved. Another benefit of antagonistic electrochemical actuators,positioned so that each can exert a force on the other, is that thestress placed on the actuators can be controlled by charging ordischarging one or both of the opposed actuators. For example, thisarrangement can allow the prestress on the actuators to be controlled tooptimize actuation force, creep, and/or the compliance of the actuator.Yet another benefit is that the positioning accuracy of the actuator isimproved when opposing actuators can be independently charged ordischarged.

Typical electrochemical cells include an electrode (e.g., an anode) thatexpands while the other (e.g., the cathode) contracts during charge, orvice-versa during discharge, in other to reduce the amount of volumechange in the cell. This can be advantageous for certain applicationssince low volume change can, for example, reduce delamination of certainlayers within the cell. However, in some embodiments of the invention,it is advantageous for both electrodes to expand during charge ordischarge, or for one electrode to not contract while the other expands.Advantageously, such configurations allow maximum energy to be used foractuation, instead of being wasted in counteracting the other electrode.

Accordingly, another embodiment includes an electrochemical cellcomprising an anode and a cathode that are constructed and arranged suchthat during a cycle in which one of the electrodes expands at least 1%by volume, the other electrode does not substantially contract. In otherembodiments, one of the electrodes expands at least 0.5% by volume, atleast 2% by volume, or at least 4% by volume, while the other electrodedoes not substantially contract. For instance, as one of the anode orcathode expands, the other can either expand, or may not change involume. A component can be in operative relationship with such anelectrochemical cell, and the component can be displaced from a firstorientation to a second orientation by charge and/or discharge of theelectrochemical cell. This simultaneous expansion of the anode andcathode, or the expansion of one electrode while the other electrodedoes not contract, can be performed by using appropriate materials forthe anode and cathode.

In some cases, an electrode may spontaneously discharge a species (e.g.,lithium), causing either an expansion or contraction of the electrodeand/or movement of one or more components of the device from a firstorientation to a second orientation. Electrode materials which exhibitspontaneous discharge are known in the art and may be advantageous incases where a particular “default” state of the device is desired, forexample, in the event of an intentional or accidental short circuit ofthe electrochemical cell.

Materials suitable for use as electrodes include electroactivematerials, such as metals, metal oxides, metal sulfides, metal nitrides,metal alloys, intermetallic compounds, other metal-containing compounds,other inorganic materials (e.g., carbon), and the like. In some cases,the electrodes may advantageously comprise materials having a highelastic modulus. In some cases, the material may be capable ofundergoing a change in volume or other dimensions upon interaction witha species, as described herein. In some embodiments, the electrodes maycomprise a material comprising a crystal structure, such as a singlecrystal or a polycrystal. In some embodiments, the electrodes maycomprise an amorphous or disordered material.

In some cases, the material forming the anode comprises one or more ofaluminum, silver, gold, boron, bismuth, gallium, germanium, indium,lead, antimony, silicon, tin. In some embodiments, the material formingthe anode may comprise Li₄ Ti₅O₁₂ or any alloy or doped compositionthereof. Examples of materials that can form the cathode include LiCoO₂,LiFePO₄, LiNiO₂, LiMnO₂, LiMn₂O₄, Li₄Ti₅O₁₂, TiSi₂, MoSi₂, WSi₂, TiS₂,or TaS₂, or any alloy or doped composition thereof. In some cases, thematerial forming the cathode may comprise TiS₂ or TaS₂. In othersembodiments, the material forming the cathode can comprise LiMPO₄, whereM is one or more first-row transition metals (e.g., Sc, Ti, V, Cr, Mn,Fe, Co, Ni, Cu, or Zn), or any alloy or doped composition thereof. Insome cases, the cathode comprises carbon, wherein the carbon may be inthe form of graphite, a carbon fiber structure, a glassy carbonstructure, a highly oriented pyrolytic graphite, a disordered carbonstructure, or a combination thereof. An electrochemical cell comprisingsuch material compositions may be operated at a cathode potentialdescribed above, e.g., less than +4V with respect to the potential ofmetallic lithium. The anode potential may be selected from thepotentials described above, e.g., greater than +0.5V with respect to thepotential of metallic lithium.

In some cases, the material forming the electrode may comprise speciesdispersed within the material. For example, the electrodes may comprisean amount of a species such that the electrode can serve as a source ofthe species within the device. In some embodiments, a substrate or othersupporting material may interact with a species to induce a volumetricor dimensional change. For example, a silicon wafer, or other metal ormetal-containing substrate may be lithiated such that a volumetric ordimensional change occurs upon charge/discharge of the electrochemicalcell.

The materials for use in electrodes of the invention may be selected toexhibit certain properties upon interaction with a species (e.g.,lithiation and de-lithiation). For example, the materials may beselected to exhibited a certain type or amount of volumetric ordimensional change (e.g., actuation) when used in an electrochemicalcell as described herein. Those of those of ordinary skill would be ableto select such materials using simple screening tests. In some cases,the properties and/or behavior of a material may be known, and one ofordinary skill in the art would be able to select materials to suit aparticular application based on, for example, the amount of volumetricchange desired. For example, reversible lithium intercalation withphospho-olivines Li(Fe,Mn)PO₄ is known to produce volume changes of7.4-10%, based on the ratio of Fe/Mn, as described in A. Yamada et al.,J. Electrochem. Soc., 148, A224 (2001). In some cases, materials may bescreened by incorporating a material as an electrode within anelectrochemical cell and observing the behavior of the material uponcharge and discharge of the cell.

In some cases, the electrode materials may be selected based on theability of a material to interact with the species. For example, wherelithium is the species, a material may be selected based on its abilityto rapidly and/or reversibly accept lithium ions (e.g., be lithiated)and/or donate lithium ions (e.g., be de-lithiated) uponcharging/discharging. Also, the corresponding strain associated withreversible interaction of the species with the material may bedetermined by knowing the rate of ion transport into the material. Suchdeterminations may be tested experimentally or made theoretically usingtabulated or estimated values of properties such as ion diffusioncoefficients, ionic and electronic conductivities, and surface reactionrate coefficients. Those of ordinary skill in the art would be able touse this information to select appropriate materials for use aselectrodes.

Electrodes may be fabricated by methods known in the art. In oneembodiment, the electrode materials may be cast from powder-basedsuspensions containing a polymer binder and/or a conductive additivesuch as carbon. The suspension may be calendered (e.g., rolled) underhigh pressure (e.g., several tons per linear inch) to form denselycompacted layers having a desired volume percentage of active material.

Materials suitable for use as an electrolyte include materials capableof functioning as a medium for the storage and transport of ions, and insome cases, as a separator between the anode and the cathode. Anyliquid, solid, or gel material capable of storing and transporting ionsmay be used, so long as the material is electrochemically and chemicallyunreactive with respect to the anode and the cathode, and the materialfacilitates the transport of ions (e.g., lithium ions) between the anodeand the cathode. The electrolyte may be electronically non-conductive toprevent short circuiting between the anode and the cathode.

The electrolyte can comprise one or more ionic electrolyte salts toprovide ionic conductivity and one or more liquid electrolyte solvents,gel polymer materials, or polymer materials. In some cases, theelectrolyte may be a non-aqueous electrolyte. Suitable non-aqueouselectrolytes may include organic electrolytes including liquidelectrolytes, gel electrolytes, and solid electrolytes. Examples ofnon-aqueous electrolytes are described by, for example, Dorniney inLithium Batteries, New Materials, Developments and Perspectives, Chapter4, pp. 137-165, Elsevier, Amsterdam (1994), and Alamgir et al. inLithium Batteries, New Materials, Developments and Perspectives, Chapter3, pp. 93-136, Elsevier, Amsterdam (1994). Examples of non-aqueousliquid electrolyte solvents include, but are not limited to, non-aqueousorganic solvents, such as, for example, N-methyl acetamide,acetonitrile, acetals, ketals, esters, carbonates, sulfones, sulfites,sulfolanes, aliphatic ethers, cyclic ethers, glymes, polyethers,phosphate esters, siloxanes, dioxolanes, N-alkylpyrrolidones,substituted derivatives thereof (e.g., halogenated derivatives thereof),and combinations thereof.

In some embodiments, electrochemical cells may further comprise abarrier or separator material (e.g., layer) positioned within the systemor device, for example, between the cathode and anode. The separator maybe a material which separates or insulates the anode and the cathodefrom each other preventing short circuiting, and which permits thetransport of ions between the anode and the cathode. Materials suitablefor use as separator materials include materials having a high elasticmodulus and/or high stiffness (e.g., rigidity), materials which areelectronically insulating, and/or materials having sufficient mechanicalstrength to withstand high pressure, weight, and/or strain (e.g., load)without loss of function. In some cases, the separator layer may beporous. Examples of separator materials include glass, ceramics, asilicate ceramic, cordierite, aluminum oxide, aluminosilicates, or othermixed-metal oxides or nitrides or carbides that are electronicallyinsulating. In some cases, the separator layer may comprise a polymericmaterial. Separator layers comprising, for example, elastomericmaterials, may be useful in allowing shearing motions between one ormore components.

In one embodiment, the porous separator material may be cast as aparticulate or slurry layer on the surfaces of one or both electrodesprior to assembly of the layers, using methods known to those ofordinary skill in the art of ceramic processing or coating technology,such as spray deposition, doctor blade coating, screen printing, webcoating, comma-reverse coating, or slot-die coating.

Devices of the invention may further comprise additional components tosuit a particular application. For example, devices of the invention maycomprise a power supply, current collector, such as a current collectorcomprising a conductive material, external packaging layers, separatorlayers, and the like. The packaging layer may comprise anelectrochemically insulating material or other protective material.

The system or devices may be optionally pretreated or processed prior touse as a an actuator. Pretreatment of the devices may enhance themechanical performance, stiffness, actuation energy density, actuationstrain, reversibility, and/or lifetime of the devices, and/or may reducecreep deformation and hysteresis of strain. In some cases, the devices,or one or more components thereof, may be subjected to hydrostaticpressure and/or uniaxial stress to consolidate the materials and/orcomponents of the device, and/or reduce the amount of free volume. Insome embodiments, the applied pressure may be 10,000 psi, 20,000 psi,30,000 psi, 45,000 psi, or greater. It should be understood that anyamount of applied pressure may be used to pretreat a device, such thatinternal failure of the device is prevented and/or improvement of deviceperformance may be achieved.

The following examples are intended to illustrate certain embodiments ofthe present invention, but are not to be construed as limiting and donot exemplify the full scope of the invention.

EXAMPLE 1 Self-Powered Electrochemical Pump

In this prophetic example, actuators of the invention can be used asself-powered electrochemical pumps for insulin therapy.

Clinical treatment of type 1 diabetics is usually insulin therapy, whereinjections of long and short acting insulin are used in combination torespond to periodic blood glucose measurements. Treatment may includeinsulin infusion pump therapy, including continuous subcutaneous insulininfusion (CSII), which dispenses rapid acting insulin from amicroprocessor controlled pump through a minute catheter. Some existingpumps can continuously dispense rapid acting insulin and may provideincremental doses before or after meals. The infusion set is changedevery three days so the effective number of injections is dramaticallyreduced over the conventional multiple daily injection (MDI) regimen.The exclusive use of rapid acting insulin yields a much improvedpredictability in dosing as the long acting forms of insulin work byforming a depot under the skin. However, insulin release rate from suchdepots can vary significantly depending on factors such as physicalactivity. Self-powered electrochemical pumps can address the problems ofreduced effective number of injections and varying insulin releaserates.

A self-powered electrochemical pump may be designed to deliver 2.0 mLpayload over a 72 hour period. FIG. 16 shows a schematic design for theself-powered electrochemical pump 350. The negative electrode 355provides a source of lithium, while the positive electrode 360 is theexpanding element. The cell is electrochemically balanced so that theavailable lithium in the negative electrode can expand the positiveelectrode. The pump can be designed for a 300% volume expansion of thepositive electrode, creating a longitudinal displacement, not unlike apiston, that delivers force to an actuation plate which in turn appliespressure to a reservoir 365 containing the insulin solution. Thevertical displacement of the positive electrode can be determined by itswidth/height aspect ratio (here assumed to be 2:1) and volume change.The electrolyte may be a standard non-aqueous lithium batteryelectrolyte. The packaging can be a polymer packaging similar to thatcurrently used for rechargeable lithium ion batteries.

Advantageously, the release rate of the insulin solution can becontrolled by choosing appropriate materials used to form the positiveelectrode. For example, for an electrochemical pump having a positiveelectrode material of relatively low stiffness, the positive electrodecan slowly displace to its new equilibrium position upon discharge. Thiscan result in a slow application of a force to the reservoir, therebycausing slow infusion of insulin to the body.

The pump may have a volume of 8.6 mL, which will allow a total devicevolume of <15 mL. The pump mass of 14.5 g should allow a total devicemass of about 20 g. With the appropriate choice of materials andelectrolyte, this pump design can deliver insulin over 72 h at the basalrate required. For the bolus rate, which corresponds to a cell dischargerate of approximately C/5 (i.e., 5 hr discharge for the entire capacityof the cell), additional design modifications can be incorporated.Additionally and/or alternatively, the pump may have similarspecifications as those for existing continuous infusion pumps. Forexample, rapid acting insulin such as the Lilly product Lispro® comespackaged as solutions with 100 units per mL concentration. Typical basalinsulin levels might be adjusted between 0.5 to 1.5 units per hour. Abolus dose for a meal might consist of 1 unit per 10 gm of carbohydrateconsumed, so as much as 10 units for a meal may be desired. Thephamacodynamics of the rapid acting insulin suggests that the dose bedelivered over 15 minutes. Any longer and one might see some differencesfrom a subcutaneous injection of the same amount. Thus, the peak rate ofdelivery is a volume of 0.1 mL in 15 minutes. A linear compression of areservoir with 6.5 cm² cross section requires 0.015 cm in 15 minutes or0.167 microns per second maximum displacement rate. The total dailypayload of insulin solution must be approximately 50 units or 0.5 mL.Thus, a three day supply requires 1.5 mL volume payload.

EXAMPLE 2 Electrochemical Actuator

In this prophetic example, an electrochemical actuator comprises abimorph structure including a layer of dimensionally-active lithiumstorage material bonded to a layer of copper. The layer of copper doesnot alloy or intercalate substantially with lithium, yet iselectrochemically stable at the operating potentials of theelectrochemical cell. This bimorph structure forms the positiveelectrode of the cell. The copper layer can also act as a positiveelectrode current collector, and may extend outside the final sealedcell to form a tab or current lead, or may be joined to a tab or currentlead that extends outside the cell. The negative electrode is a layer oflithium metal bonded to or deposited on a copper layer serving as thenegative current collector. Between the two electrodes is positioned aporous separator film, e.g., a glass fiber cloth or a porous polymerseparator such as those used in the construction of lithium ionbatteries. The layered cell is infused with a nonaqueouslithium-conducting liquid electrolyte such as is commonly used inlithium primary or rechargeable battery technology, or nonaqueouselectrical double layer capacitors. Examples include a solventcomprising a 1:1 by volume mixture of ethylene carbonate and diethylenecarbonate, to which has been added a 1M concentration of LiPF₆ as alithium conducting salt, or acetonitrile as a solvent to which has beenadded the same LiPF₆ salt.

The electrochemical actuator is sealed in a polymer packaging. Uponassembly, the cell is in a charged state, with the tin positiveelectrode having a lower chemical potential for lithium than the lithiummetal negative electrode. Upon connecting the negative and positivecurrent collectors so that electronic current flows between the twoelectrodes, a lithium ion current flows internally from the lithium tothe tin. The alloying of the tin with lithium results in a volumeexpansion that may reach nearly 300% when the tin is saturated withlithium. As the tin layer increases in volume due to alloying withlithium, the copper layer to which it is bonded provides a mechanicalconstraint, and the bimorph undergoes displacement (e.g., bending). Atthe negative electrode, the loss of lithium may result in a small stressas well, but this stress is much less than that of the positiveelectrode since lithium is highly ductile near room temperature. Thus,the entire cell undergoes flexure due to the volume change of the tinlayer on the electrochemical actuator comprising the positive electrode.Flexure of the cell in turn applies a pressure to a drug reservoir,which is positioned adjacent the actuator. The drug reservoir contains afluid comprising a drug and is enclosed by a deformable vessel such as abladder. The applied pressure causes the drug to be dispensed from thereservoir.

EXAMPLE 3 Electrochemical Bimorph Flexure

In this prophetic example, the bimorph structure of EXAMPLE 2 isfabricated in the shape of a semicircle or “U” shaped flexure as shownin FIGS. 3A-C. One end of the flexure is anchored to a support orhousing of the dispensing device, while the other end is free todisplace as the bimorph undergoes flexure. Upon discharge of theelectrochemical cell, the flexure extends outwards, and the free end ofthe flexure applies a force to a drug-containing bladder, dispensing adrug through an orifice or valve from the bladder.

EXAMPLE 4 Self-Powered Morphing Actuator with Built-In Amplification

In this Example, an electrochemical cell was fabricated and was studiedfor its ability to actuate upon application of a voltage or current. Aporous pellet was pressed from −325 mesh tin powder (99.8% [metalsbasis], Alfa Aesar) in a ½-inch diameter die under 750 lbf. The pelletweighed 0.625 g and was measured to have a thickness of 0.89 mm. Thepellet was soldered to copper foil of 15 micrometer thickness usingBiSnAg solder (Indium Corporation of America) and flux #5RMA (IndiumCorporation of America) by heating the assembly in an air furnace at180° C. for 30 minutes. This electrode assembly was used as the positiveelectrode in an electrochemical cell, while lithium foil (˜0.8 mmthickness, Aldrich) was used as the negative electrode.

Two layers of Celgard 2400 separator were used to separate the tinpositive electrode and the lithium foil negative electrode. The lithiumfoil electrode was attached to a current collector made also from the 15micron thick copper foil. A liquid electrolyte consisting of 1.33 MLiPF₆ dissolved in a mixed solvent of ethylene carbonate, propylenecarbonate, dimethyl carbonate, and ethyl methyl carbonate (4:1:3:2 byvolume) was used. The cell was sealed in an envelope made ofpolyethylene bagging material using a heat sealer. Upon assembly theopen circuit voltage of the cell was 2.8-2.9V, showing that it was inthe charged state. Upon discharge the cell voltage dropped rapidly to arelatively constant value of 0.5-0.4V, as is characteristic of the Sn—Lielectrochemical couple.

The cell was discharged across a 1 ohm resistor that connected thepositive and negative current collectors. The displacement measurednormal to the plane of the tin disc and lithium foil while the celldischarged was measured using a linear variable differential transformer(LVDT) from Micro-Epsilon. Readings were measured through a NationalInstruments NI-USB 6009 data acquisition device interfaced with LabView(National Instruments). FIG. 17 shows a graph of the resultingdisplacement from this experiment as a function of time.

After an initial small compression caused by the lithium and separatoryielding under the small applied force of the LVDT, the actuatorextended by 1.8 mm as it discharged over a period of 11 hours. Thisabsolute displacement exceeded the initial thickness of the Sn pellet byabout a factor of two. Inspection of the disassembled actuator after thetest showed that discharge had occurred, with lithium being eroded fromthe negative electrode and alloying with the tin pellet from one side.It was readily observed that the displacement of the actuator was due tothe cylindrical tin pellet deforming into a “cupped” shape with theconvex surface being the side facing the separator and lithiumelectrode. Thus, it was seen that the shape-morphing of the tin pelletwas due to the creation of a differential strain across the pellet, withthe side facing the lithium electrode undergoing expansion. Mechanicalloading in the direction of displacement normal to the plane of thepellet after deformation showed that a load of more than 1 kg could besupported without fracture of the deformed pellet. Thus, the actuatorhas substantial stiffness, which would be useful for applications suchas the dispensing or pumping of a fluid-filled bladder, as in a drugdelivery applications where the fluid may be dispensed through one ormore needles or microneedles. By placing the actuator of this example inproximity to such a fluid-filled bladder, and enclosing the whole in arigid container, a drug delivery device could be obtained.

Such a drug delivery device would be suitable, for example, for a 3-day(72 h) delivery of insulin. Rapid acting insulin such as the Lillyproduct Lispro® are generally packaged as solutions with 100 units permL concentration. The total daily payload of insulin solution may beapproximately 50 units or 0.5 mL. Thus, a pump with a three day supplycan accommodate a total volume of ˜2.0 mL. For example, the actuatordescribed in this Example produced a displacement of more than 1.5 mm,which, when acting on a reservoir of 13 cm² area, can easily obtain thedesired 2.0 mL volume. Typical basal insulin levels might be adjustedbetween 0.5 to 1.5 units per hour. A bolus dose for a meal might consistof 1 unit per 10 gm of carbohydrate consumed, so as much as 10 units fora meal may be desired. The phamacodynamics of the rapid acting insulinsuggests that the dose can be delivered over 15 minutes. Thus, the peakrate of delivery may correspond to 5% of the total volume over 15minutes. Taking a displacement of 1.5 mm to correspond to completedelivery of a 2 mL insulin payload, the actuator in this Example canreadily meet the bolus rate requirement. In order to slow down the rateto meet the basal rate requirement, an increase in resistance of theexternal load or duty cycle control, as described below in Example 7,can be implemented.

This Example may demonstrate the electrochemical actuator and drugdelivery device in certain embodiments of the invention, bydemonstrating electrochemical actuation due to the creation ofdifferential strain across an electrode. Consideration of the net volumechange of the actuator during discharge of the cell showed that thedisplacement obtained was not correlated with the net volume change, andwas in fact opposite in sign to the net volume change of the cell.Comparing the partial molar volume of lithium in various Li_(x)Sn alloyswith the molar volume of pure lithium, it was observed that pure lithiumhad a larger molar volume and therefore discharge of a cell in whichlithium was the negative electrode resulted in a net volume decrease.For example, Li_(2.5)Sn, a compound of relatively low Li/Snstoichiometry, has a molar volume of 38.73 cm³ mol⁻¹. Since pure Snmetal has a molar volume of 16.24 cm³ mol⁻¹, the difference, 22.49 cm³mol⁻¹, of the compound was the volume occupied by the 2.5 Li inLi_(2.5)Sn. In comparison, the molar volume of pure Li was 13.10 cm³mol⁻¹, such that 2.5 moles of Li metal would have a volume of 32.75 cm³.Therefore, complete discharge of a cell to form Li_(2.5)Sn on thepositive electrode side would result in the transfer of 2.5 moles oflithium from the Li electrode to the Sn, resulting in a net decrease inthe volume of the device. Similarly, the molar volume of Li inLi_(4.4)Sn, a compound of relatively high stoichiometry, is 42.01 cm³mol⁻¹, whereas 4.4 moles of pure Li metal has a volume of 57.62 cm³mol⁻¹. Again, the discharge of such a cell resulted in a net volumedecrease. The outward or positive displacement observed in the actuatorof this Example occurred despite the negative volume change upondischarge. The flexure or “cupping” mode of deformation of the actuatoramplified the deformation due to differential strain across the pellet.

EXAMPLE 5 Galvanostatic Discharge of an Electrochemical Actuator

In the following example, the galvanostatic discharge of anelectrochemical cell was studied. An electrochemical cell as describedin Example 4 was fabricated, with conductive copper adhesive tape usedas the contact between the porous tin pellet and the copper currentcollector, instead of solder. The cell was galvanostatically discharged(constant discharge current) using a Maccor 4300 battery tester(Maccor). The tin pellet weighed 0.628 g and was measured to have athickness of 1.06 mm. The theoretical capacity of the pellet was 624mAh, assuming all of the tin was lithiated to the compound Li_(4.4)Sn.Upon assembly the open circuit voltage of the cell was 2.8-2.9V, showingthat it was in the charged state. The cell was discharged at 0.88 mA to0.01V, The discharge capacity was 56.22 mAh, showing that the cell wasdischarged to only 9% of its theoretical capacity over the dischargetime of 63.6 h. However, the Sn pellet was observed to have cupped inthe same manner and to approximately the same deformation as theactuator in Example 1. This Example demonstrated the current-limitedcontrol of an electrochemical actuator which can spontaneously dischargeand actuate if the positive and negative leads were closed in anexternal circuit.

EXAMPLE 6 Electrochemical Bimorph Actuators

A bimorph electrode was fabricated by masking one side of a copper foilof 50 micrometer thickness and 40 mm×5 mm area with Kapton® adhesivetape and dipping the foil in molten tin to coat one side with a layer oftin. It was expected that upon electrochemical lithiation of the tin,the constraint provided by the copper foil would result in bending or“curling” of the bimorph structure with the convex side being thelithiated tin. An electrochemical cell like those in Examples 4 and 5was assembled using this bimorph as the positive electrode, assembledwith the tin layer facing the separator and lithium foil negativeelectrode. Upon assembly, the open circuit voltage of the cell was2.8-2.9V, showing that the cell was in the charged state. The cell wasgalvanostatically discharged to 0.01 V with a current of 0.089 mA. Thedischarge capacity was 7.7 mAh, representing about 50%state-of-discharge for a tin layer thickness of about 10 micrometers andassuming a fully lithiated composition of Li_(4.4)Sn.). After discharge,the cell was disassembled, and the tin-copper bimorph electrode showedsubstantial bending at all free edges of the bimorph, demonstratingshape-morphing.

In other experiments, tin metal foil samples of 0.05 mm (99.999% [metalsbasis], Alfa Aesar) and 0.10 mm (99.99% [metals basis], Alfa Aesar)thickness were each joined to 15 micrometer thick copper foil, formingflat bimorph electrodes of 20 mm×5 mm area. Electrochemical cells wereconstructed using two layers of Celgard 2400 separator to separate thetin/copper bimorph positive electrode and a 0.4 mm thick lithium foil(Aldrich) negative electrode. For each cell, the lithium foil electrodewas attached to a current collector made also from the 15 micron thickcopper foil, and a liquid electrolyte consisting of 1.33 M LiPF₆dissolved in a mixed solvent of ethylene carbonate, propylene carbonate,dimethyl carbonate, and ethyl methyl carbonate (4:1:3:2 by volume) wasused. Each cell was sealed in an envelope made of polyethylene baggingmaterial using a heat sealer.

The cells were discharged galvanostatically using a Maccor 4300 batterytester (Maccor). The cell made using 0.10 mm thick tin foil wasdischarged at 0.4178 mA to 0.01V. The discharge capacity was 1.65 mAh(4% of the theoretical discharge capacity). The discharge profile forthis device is shown in FIG. 19. Upon disassembly, the bimorph electrodewas observed to have “curled” at all free edges, demonstrating severemorphing.

The cell made using 0.05 mm tin foil was discharged at 0.4076 mA untilthe discharge capacity was 1.65 mAh (4% of the theoretical capacity).The discharge profile for this device is shown in FIG. 20. Similar tothe 0.10 mm tin foil bimorph, this device upon disassembly also showedbending at all free edges of the bimorph.

These examples demonstrated various electrochemical bimorph actuators ofthe invention. These results also show that it may not necessary tofully discharge the electrochemical cells of the invention in order toobtain significant morphing, but that the differential strain resultingfrom only a few percent discharge of the theoretical cell capacity maybe sufficient to achieve desired actuation.

EXAMPLE 7 Duty Cycle Control of an Electrochemical Actuator

An electrochemical actuator of similar design to that described inExample 1 was subjected to duty cycle controlled discharge in order toobtain a slow deformation rate. The duty cycle was controlled by anelectronic relay (Radio Shack), which was switched on and off throughcurrent control from a Maccor 4300 battery tester (Maccor), connected inseries with the 1 ohm external load resistor across the terminals of theelectrochemical cell. The relay closed while receiving current from thebattery tester and opened when the current was interrupted. A 20% dutycycle was configured, in which the current was turned on for 50 ms outof a total period of 200 ms. FIG. 18 shows a graph of the displacementcurve for the electrochemical morphing actuator, controlled by a 20%duty cycle. The resulting displacement of the device, shown in FIG. 18,demonstrated deformation of the actuator at a low controlled rate. Asdescribed herein, an alternative method of obtaining a controlled lowrate of deformation may be to discharge the actuator in FIG. 18 througha higher resistance external load.

EXAMPLE 8 A Self-Powered Electrochemical Actuator Having Larger DrivingVoltage

Under some circumstances a higher average discharge voltage than thatfor the preceding examples utilizing tin and lithium metal may bedesirable, such as when a substantial driving voltage is needed, even inthe presence of significant cell polarization. Antimony can be a usefulmorphing electrode material for such applications due to its relativelylarger open circuit voltage vs. lithium metal (˜0.95V).

An electrochemical device was prepared as in Example 1, using −325 meshantimony powder (99.5% [metals basis], Alfa Aesar) instead of the tinpowder. The antimony powder was pressed at 2250 lbf in a ½ inch diameterdie. The resulting pellet was 0.687 g and 1.31 mm thick, correspondingto a theoretical capacity of 454 mAh. The sample was galvanostaticallydischarged at a current of 3.025 mA to 0.01V. The discharge capacity was49.98 mAh (11% of theoretical capacity), and resulted in severedeformation of the antimony pellet.

EXAMPLE 9 Self-Amplifying Circular Plate Actuator

A ¾ inch diameter circular disc was punched from a 1 mm thick tin plate(Alfa

Aesar) to be used as the positive electrode in an electrochemical cell.A 15 micrometer thick copper foil current collector was spot-welded toone face of the tin disc. A negative electrode also in the shape of a ¾inch diameter disc was punched from a lithium metal sheet (Alfa Aesar),and a 15 micrometer thick copper foil current collector was attached tothe lithium foil. A sheet of glass fiber filter paper was used as aseparator between the two electrodes. The electrodes and separator wereassembled in a sandwich configuration with the edges of the two discelectrodes being aligned and held in place using Kapton® tape. Thisassembly was placed in a pouch made of polymer sheet used for lithiumbattery packaging, a conventional lithium battery liquid electrolyteconsisting of LiPF₆ dissolved in a mixture of alkyl carbonates wasadded, and the cell was evacuated and heat-sealed.

The cell was discharged by connecting it in series with a 10 Ohmresistor. This caused lithium ions and electrons to be produced at thenegative electrode and recombine at the positive electrode, alloyingwith the tin electrode to form a thin surface layer of a Li—Snintermetallic phase at the surface of the tin disc facing the separator.Due to the softness of the Li electrode, the deformation of the actuatorwas predominantly determined by the deformation of the tin electrode.The laminated discs cupped into the shape of a spherical cap upondischarge, producing an outward displacement at the center of the discsand in their axial direction, the outwards displacement being towardsthe side of the actuator having the Li metal electrode. The displacementreached 2 mm over a discharge time of about 8 hours in thisconfiguration.

EXAMPLE 10 Actuator with Electrodes Masked to Limit the RegionsUndergoing Lithium Reaction

A ½ inch diameter circular disc was punched from a 1 mm thick tin plate(Alfa Aesar) to be used as the positive electrode in an electrochemicalcell. One face and the edges were sputtered with copper, copper being ametal with which Li does not typically react, and which therefore servedto prevent reaction with lithium at the faces where it is sputtered. A15 micrometer thick copper foil current collector, 15 microns thick, wasspot-welded to the copper-sputtered face of the tin disc. A negativeelectrode also in the shape of a ½ inch diameter disc was punched from alithium metal sheet (Alfa Aesar), and a 15 micrometer thick copper foilcurrent collector was attached to the lithium foil. A sheet of Celgard2400 separator (Celgard) was used between the two electrodes. Theelectrodes and separator were assembled in a sandwich configuration withthe edges of the two disc electrodes being aligned and held in placeusing Kapton® tape. This assembly was placed in a pouch made ofpolyethylene-based packaging material and a conventional lithium batteryliquid electrolyte consisting of LiPF₆ dissolved in a mixture of alkylsolvents was added, and the cell was evacuated and heat-sealed.

The cell was discharged by connecting it in series with a 10 Ohmresistor. This caused lithium ions and electrons to be produced at thenegative electrode and recombine at the positive electrode, alloyingwith the tin electrode to form a thin surface layer of a Li—Snintermetallic phase at the surface of the tin disc facing the separator.Due to the softness of the Li electrode, the deformation of the actuatorwas predominantly determined by the deformation of the tin electrode.The laminated discs cupped into the shape of a spherical cap upondischarge, producing an outward displacement at the center of the discsand in their axial direction, the outwards displacement being towardsthe side of the actuator having the Li metal electrode. The coppersputtered film prevented significant lithium alloying at the sputteredsurfaces, demonstrating control of the lithium reaction regions on thetin positive electrode through masking by a nonreactive material.

EXAMPLE 11 Actuator with Electrode Design for Improved StrainAmplification

An electrochemical cell was constructed according to the methoddescribed in Example 10, except that the tin positive electrode was madelarger than the lithium negative electrode. A 1 inch×1 inch square pieceof 1 mm thick tin (Alfa Aesar) was used for the positive electrode. A ½inch diameter disc of lithium serving as the negative electrode wascentered on the 1 inch square tin plate electrode and secured withKapton® tape. During discharge of this cell, the lithium alloyingreaction was generally limited to the central region of the tinelectrode in close proximity to the lithium electrode. Lithium alloyingat the surface of the tin sheet caused cupping of the circular region inclosest proximity to the lithium disc. However, the deformation of thisregion also caused the unreacted portions of the tin plate to deform,resulting in a large strain amplification as shown by the photographs inFIGS. 21A-B.

This resulted in a greater net displacement at the center of theactuator than obtained in Example 10 for the same extent of discharge.The graph shown in FIG. 21C compares the displacement obtained from the½ inch diameter disc actuator in Example 10 with that from the 1″ squareelectrode actuators of this Example. It was observed that, at the sameextent of discharge (measured as discharge capacity in mAh), thedisplacement of the oversized square electrode is significantly greater.

EXAMPLE 12 Radially Symmetric and Two-Fold Symmetric Actuators andControl of Deformation Load by the Application of Preload

In the devices described in Examples 9 and 10, the deformation of theactuator upon discharge was approximately radially symmetric. However,through modifications in the design of the actuators or by allowinglarger extent of reaction the deformation of the tin sheet electrodes,mechanical instabilities can be produced resulting in a lower symmetryof folding such as is illustrated by the photographs in FIG. 22. FIG. 22shows (a) a photograph of a folded actuator with no external load and(b) a photograph of an actuator, wherein suppression of folding motionoccurs with the application of an external load to produce a radiallysymmetric actuator. In FIG. 22A, the actuator folded along one axis,producing a larger displacement along the axial direction of the discsthan those shown in FIG. 22B, where the deformation was radiallysymmetric.

The deformation mode of the actuator was also controlled by thecontrolled application of load. As shown in FIG. 22B, the foldinginstability illustrated by the actuator in FIG. 22A was reduced orprevented by application of a load of about 50-100 g to the actuatorwhile it underwent actuation. The actuators described in this Examplewere fabricated using the method described in Example 10, except thatthe tin electrodes were not masked with sputtered copper.

EXAMPLE 13 Three-Fold Symmetric Actuator

A ¾ inch diameter disc was punched out of 1 mm thick tin plate. The discwas cut to produce a central triangular region with three protrudingsections. FIG. 23 shows a photograph of this three-fold symmetricelectrode for use as an electrochemical actuator. A ½ inch diameterlithium metal disc electrode was placed over the central region, and theelectrochemical cell was otherwise fabricated as described in Example 10except that copper sputtering to mask the tin electrode was not used.Similarly, the device was discharged through a series connection with a10 ohm resistor.

FIG. 24 shows a graph of the displacement and current versus time duringdischarge for a three-fold symmetric electrode actuator. FIG. 25 shows aphotograph of a three-fold symmetric tin electrode actuator, afterdischarge. The three-fold symmetry and protruding sections combined togive strain amplification similar to that of a larger tin plate with asmaller lithium electrode, as shown in FIG. 24, while the ends of thethree “legs” define a plane and permit stable bearing against a planarsurface, as shown in FIG. 25. It is understood that other methods couldbe utilized to achieve actuation with a three-fold symmetry, includingbut not limited to the use of a three-fold symmetrically shaped lithiumelectrode, or by masking the tin electrode to limit the lithium alloyingto an area of three-fold symmetry. Masking could be also be performed bysputtering a lithium-passivating material such as copper, or by using anelectrochemically stable masking material such as Kapton® tape appliedto the surface of the electrode.

EXAMPLE 14 Folding Actuator

A ¾ inch diameter circular disc was punched from a 1 mm thick aluminumplate (Alfa Aesar) to be used as the positive electrode in anelectrochemical cell. One face of the disc was then masked to produce acenter exposed strip of aluminum. The masking process involved applyinga ¼-inch wide strip of Kapton® tape across the diameter of the aluminumdisc and spray-painting the disc with Krylon®. The tape was then removedso that the only exposed portion of the aluminum disc was the ¼-inchwide strip that had been under the Kapton® tape during spray-painting.(FIG. 27A) A 15 micrometer thick copper foil current collector wasspot-welded to the opposing face of the aluminum disc. A negativeelectrode also in the shape of a ¾ inch diameter disc was punched from alithium metal sheet (Alfa Aesar), and a 15 micrometer thick copper foilcurrent collector was attached to the lithium foil. A sheet of Whatmanglass fiber filter paper was used as a separator between the twoelectrodes. The electrodes were assembled with the masked face of thealuminum electrode facing the lithium electrode, and with the separatorarranged in between the electrodes. This assembly was placed in a pouchmade of polymer sheet used for lithium battery packaging, a conventionallithium battery liquid electrolyte consisting of LiPF₆ dissolved in amixture of alkyl carbonates was added, and the cell was evacuated andheat-sealed. As-assembled, the cell was in a charged state.

The cell was discharged by connecting the positive and negative currentcollectors in series with a 10 Ohm resistor, allowing electrical currentto flow between the electrodes. As a result, lithium ions weretransported from the negative electrode across the separator to thepositive electrode, reacting with the ¼ inch wide strip of exposedaluminum to form a thin surface layer of Li—Al intermetallic phase. Upondoing so, the aluminum disc and the entire electrochemical cell wasobserved to fold around an axis lying in the plane of the surface of thealuminum electrode and aligned with the long axis of the exposedaluminum strip. FIG. 28 shows a photograph of the final, foldedactuator. The folding of the electrochemical cell resulted in adisplacement, measured normal to the axis of the disc, of about 3.5 mmover a discharge time of 10 hours, FIG. 29 shows a graph of thedisplacement vs. time for two aluminum disc samples, assembled anddischarged as described in this example. After an initial incubationtime of small displacement, the displacement is observed to be nearlylinear with time.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Other elements may optionallybe present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elementsspecifically identified unless clearly indicated to the contrary. Thus,as a non-limiting example, a reference to “A and/or B,” when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A without B (optionally including elements other thanB); in another embodiment, to B without A (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

1-82. (canceled)
 83. An actuator system constructed and arranged to bedisplaced from a first orientation to a second orientation, comprising:an electrochemical cell including a negative electrode and a positiveelectrode, wherein at least one of the negative electrode and thepositive electrode is an actuator, the actuator including a firstportion and a second portion, and the first and second portions arrangedsuch that the electrode has at least a two-fold symmetry when viewednormal to a surface of the actuator.
 84. The actuator system of claim83, wherein the actuator has three-fold symmetry when viewed normal to asurface of the actuator.
 85. The actuator system of claim 83, whereinthe actuator has four-fold symmetry when viewed normal to a surface ofthe actuator.
 86. The actuator system of claim 83, further comprising: aspecies formulated to intercalate, de-intercalate, alloy with, oxidize,reduce, or plate with the first portion of the actuator to an extentdifferent than the second portion of the actuator, thereby imparting adifferential strain between the first and second portions and causing adisplacement of at least a portion of the actuator.
 87. The actuatorsystem of claim 86, wherein the species intercalates as theelectrochemical cell is allowed to discharge from its initially chargedstate.
 88. The actuator system of claim 86, wherein the actuator issubstantially rectangular and the displacement occurs along an axis thatis parallel to an edge of the actuator.
 89. The actuator system of claim86, wherein the actuator is substantially circular and the displacementoccurs along axes having three-fold symmetry when viewed normal to thesurface of the actuator.
 90. An electrochemical actuator, comprising: anelectrode serving as a donor of an intercalating species; and acounterelectrode serving as an acceptor of the intercalating species,the counterelectrode having a first portion configured to inhibitintercalation of the species and a second portion configured to allowintercalation of the species to an extent greater than the firstportion.
 91. The electrochemical actuator of claim 90, wherein the firstportion is a masked portion and the second portion is exposed portion.92. The electrochemical actuator of claim 91, wherein the masked portionis a first surface of the counterelectrode and the exposed portion is asecond surface of the counterelectrode opposing the first surface. 93.The electrochemical actuator of claim 92, wherein the first surface ofthe counterelectrode faces away from the electrode and the secondsurface of the counterelectrode faces the electrode.
 94. Theelectrochemical actuator of claim 91, wherein the exposed portion ispositioned near the center of a surface of the counterelectrode and themasked portion surrounded the exposed portion.
 95. The electrochemicalactuator of claim 91, wherein the counterelectrode is substantiallyrectangular and the exposed portion is positioned along an axis that isparallel to an edge of the counterelectrode.
 96. The electrochemicalactuator of claim 91, wherein the counterelectrode is substantiallyrectangular and the exposed portion is positioned along an axis that isparallel to an edge of the counterelectrode, such that the maskedportion may act as a lever to amplify the total displacement of theactuator.
 97. The electrochemical actuator of claim 91, wherein thecounterelectrode is substantially rectangular and the exposed portion ispositioned along a center axis of the counterelectrode, such that themasked portion may act as a lever to amplify the total displacement ofthe actuator.
 98. A method of fabricating an actuator, comprising:masking a portion of one surface of a first electrode to create a regionconfigured to inhibit intercalation of a species; placing a separatoradjacent the surface of the first electrode having the region configuredto inhibit intercalation of a species; placing a second electrodeadjacent the separator; and sealing the first electrode, the separator,the second electrode and an electrolyte in a pouch.
 99. The method ofclaim 98, further comprising: attaching current collectors to the firstand second electrodes such that the current collectors extend outside ofthe pouch after the pouch is sealed.
 100. The method of claim 98,wherein the fabricated actuator is in a charged state.
 101. The methodof claim 98, wherein the masking produces an exposed portion along acenter axis of the first electrode, the exposed portion configured toallow intercalation to a greater extent than the region configured toinhibit intercalation of the species.
 102. The method of claim 98,wherein the masking produces an exposed portion along an axis that isparallel to an edge of the first electrode, the exposed portionconfigured to allow intercalation to a greater extent than the regionconfigured to inhibit intercalation of the species.